<span></span><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">안녕하세요 과게 여러분들, 저는 몇 년 전부터 오유를 눈팅만 해오던 유저 입니다. 지금 올리는 글이 제가 오유에 가입하고 나서 올리는 첫 글입니다. 저는 앞으로 고등학교 수준의 물리를 설명하는 시리즈들을 올릴 생각입니다. 제가 아직 고등학생이고 외국에 살아서 정보나 한국어로 글을 쓰는 데에 부족한 점이 많습니다. 따라서 어떤 유형의 지적이든(잘못된 정보, 문맥, 가독성 또는 설명하는 방법 등) 여러분들의 지적을 환영합니다. </span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">오늘 올리는 글은 파일럿으로써, 에너지 보존 법칙과 운동량 보존 법칙을 역학 적으로, 어떤 두 물체의 충돌을 예로 설명 드릴 것 입니다. 제 글은 물리 법칙 또는 현상을 설명하는 파트와 수식을 이용해서 계산을 하여 문제를 푸는 파트로 이루어져 있습니다. 제가 수학 없이는 물리를 설명할 수 없다고 생각하기에 수학의 비중이 클 것 같습니다. 하지만 여기서 사용되는 수학은 중고등학교 수준이므로 다른 분들도 모두 이해 하시리라 생각합니다. 그러면 이제 오늘의 주제인 에너지 및 운동량 보존 법칙으로 넘어 가도록 하겠습니다.</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:24px;font-family:Arial;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">에너지 보존 법칙</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">위키백과에서는 에너지 보존 법칙을 이렇게 설명하고 있습니다.</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-style:italic;vertical-align:baseline;white-space:pre-wrap;">“열 역학 제 1법칙 이라고도 불린다. 외계에 접촉이 없을때 고립계에서 에너지의 총합을 일정하다는 것으로 물리학의 바탕이되는 법칙 중 하나다. 이 법칙에 따르면 에너지는 그 형태를 바꾸거나 다른 곳으로 전달할 수 있을 뿐 생성되거나 사라질 수 없다. 항상 일정하게 유지된다는 것이다.” </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">출처:</span><a target="_blank" href="https://ko.wikipedia.org/wiki/%EC%97%90%EB%84%88%EC%A7%80_%EB%B3%B4%EC%A1%B4_%EB%B2%95%EC%B9%99" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#1155cc;text-decoration:underline;vertical-align:baseline;white-space:pre-wrap;">https://ko.wikipedia.org/wiki/에너지_보존_법칙</span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">즉 닫힌 계에서 의 에너지  총합은 항상 같으며 에너지는 새로 만들어지거나 사라질 수 없다는 뜻입니다. 물리에서 에너지란 일을 할 수 있는 능력을 나타냅니다. </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">에너지(Energy)의 공식 기호는 E이며, 에너지의 단위는 1J입니다.</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">에너지(Energy)</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">공식 기호: E</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">단위:          </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=1J%3D1%5Cfrac%7Bkg*m%5E2%7D%7Bs%5E2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/eFdiJXXT5f3BRrW8V2sbGaQ7pugJozOxy9fZOumDmIcx-qIWGlu6LWnLuoRynGHwAlffzeqLLOQ8SFFwpPfvx6KgoArvv7UqBY3YfaT00FwpTS9Uqd-Z8xrmr7-hLqLyLDY2yCo" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">어떤 두 구체가 서로 충돌 한다고 가정 해 봅시다.</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://docs.google.com/drawings/d/sl8JZp4K0CuF3VXbVxnmxwg/image?w=283&h=129&rev=56&ac=1" style="border:none;" alt=""></span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">그리고 이 두 물체의 질량을 각각 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B1%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/hUZCUkt-j5_Q7IMUMXG48j354wW0afJtzoPNkMZ6kMEPkymgXufasKvIXua4ID7nNmcQBmrq3K0apUdLlvKHYP9amC4Hrvb0TKQS2RTAYqIE86mWmoCayGHyTuyNig89Hy453ik" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">과 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/BtEJjT0Y_EFGnkP0nv7lnq3Ge7neGGVzTnpSKZkYTohKWY2VBXgQxjwFbiIGEes3Qigpbocrnbuco6J6A7D6PxCRCHTQITF_u3lnpl5dsVjbYqlLvEkPkR5aKKOVdkLqxo6lKHs" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">라고 하고 이 두 물체의 충돌 전 속도 또한 각각 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/P0tEHZlDKg1-ud-Ya58aVW04q1U9cOIMHuc94-2gJBZi_cBCI5Mo2-vHI7R8xAVs5YI2Y92GgW1MvrJiH4FAiZnkusOF5SXjZ5K96tnn5gv5Y6Cf0-2J0VKf29zmuOSo7a_ReXw" style="border:none;" alt=""></span></a><span style="font-size:14.6666666666667px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">과 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B2%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/32r_977XuFWa3czJaSI2ZXI-xOSuyNLfRxEA6WRAsfpE94LFq6MhLqRMo-CM_EQBZnLwxsCpsYOkd18qYWgU7IbtVc7Xyrn3U5nNCes4ewGtnzNc5Mp-Y_T5SUNqD8JsZL-mgQM" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">라고 합시다. (속도 v의 위에 화살표가 있는 것은 속도가 벡터임을 나타냅니다. 벡터(vector)란 방향과 크기를 둘 다 가지고 있는 물리량으로 예를 들어 힘, 속도, 운동량 등이 있습니다. 반대로 방향이 없이 크기만 가지고 있는 물리량을 스칼라(scalar)라고 하며 예를 들어 온도,질량 등이 있습니다.)</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">그리고 충돌 후 두 물체의 속도를 각각 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bu_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/NqZm_wxi6j5nxN_TgtiVr4cmHYXNePVWoig7UaiDTz2Dd00hs-z81-m16mDGiWu84ykX7D1v3ECZ-Rf9GO6hqXQnlPvjjHSWnnuIfrkzMpZ_6-Tjvr9unAxaPYM8VgUVPHqt63s" style="border:none;" alt=""></span></a><span style="font-size:14.6666666666667px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">과 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bu_%7B2%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/8WnUZQFAb_Ya_YZh4F-kfJAlcEwUNLEuQ9L8_XaS137PxWIvW0fuRl_wIJJPOg7B5WTY4RE7VeIaS2wOEWiacyzkosSH75s3decn7R4NcRAoKPzaYE7CwJ7revd6vnZExSUac90" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"> 라고 합시다.</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://docs.google.com/drawings/d/s8iyhjEc1c179qrdzVFKy0g/image?w=234&h=58&rev=24&ac=1" style="border:none;" alt=""></span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">에너지 보존 법칙에 따르면 이 계가 닫힌 계라고 가정하면 충돌 전의 에너지와 충돌 후의 두 물체가 가진 에너지는 같아야 합니다. 즉:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">E</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">충돌 전</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">=</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">E</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">충돌 후</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">가 성립합니다. 그리고 이 식에 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=E%3D%5Cfrac%7B1%7D%7B2%7D*m*v%5E%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh3.googleusercontent.com/2SST-ej7FOcapBra2gg1SIb5HvIsEmWoV179wumSTdd0Nr-DsO30M4fabNPyRzLhTEt740h2IFYxNvjRTZGjzATtx_iHj648dhoXqd0Y7EdOY9lDkXgaOTkw5nDxUme5rihbTtk" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"> 을 대입하면:</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cfrac%7B1%7D%7B2%7D*m_%7B1%7D*v_%7B1%7D%5E%7B2%7D%2B%5Cfrac%7B1%7D%7B2%7D*m_%7B2%7D*v_%7B2%7D%5E%7B2%7D%3D%5Cfrac%7B1%7D%7B2%7D*m_%7B1%7D*u_%7B1%7D%5E%7B2%7D%2B%5Cfrac%7B1%7D%7B2%7D*m_%7B2%7D*u_%7B2%7D%5E%7B2" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/GkHXIP8cVuDCEG_O_iaNKZ96_pOc7SOhoIGJmP_1TQC-WjU5wzxUOWIIHPfQcbV3GWyRJXoenS8h7HR_2HBNU8YxDobHN2bg8IcU0j_yfm_McD10pvDe86Ace6MQTUf6JTPcRk0" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">가 됩니다. 이 공식이 에너지 보존 법칙 공식입니다.</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:24px;font-family:Arial;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">운동량 보존 법칙</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">고전역학에서 운동량은 질량과 속도의 곱이며, 속도와 마찬가지로 운동량도 방향과 크기를 둘 다 갖고 있는 벡터입니다.</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bp%7D%3Dm%5Cstackrel%7B%5Crightarrow%7D%7Bv%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#000000;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;"><img src="https://lh6.googleusercontent.com/8u19J1sdaNYF58O8szOyt_1f2an8_-kozTDQPXTAf1wmcRa8e8zkZPpoWFut00ln_QX-ISWIiNteEFqnd4LHeXUJmUBfHqayv6Gt1w_l3kzLqif-vaL4NqM5-_l-bIbZUPvwuBM" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">운동량(Momentum)</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">공식 기호: p</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">단위: </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=1%5Cfrac%7Bkg%7D%7Bm*s%7D%3D%201N*s" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh3.googleusercontent.com/KchisHfbsvIr5u7n8IQtdhyayIpVW3Z6s4TxnEbQQtilWNBF1xkpg3Odu2qqsC-LGPsfwIHWkHF6ELVTa02dgoE-FOQAjU5_hRGcHQeH_b1RklTcM6w08MXc7B_l2R95awZfw90" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">에너지 보존 법칙과 마찬가지로 운동량 보존 법칙에서도 충돌 전의 두 물체가 가지고 있는 운동량과 충돌 후의 운동량의 값이 같습니다. 따라서</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">p</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">충돌 전</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">=</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">p</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">충돌 후</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">가 성립합니다. 여기에 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bp%7D%3Dm%5Cstackrel%7B%5Crightarrow%7D%7Bv%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#000000;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;"><img src="https://lh6.googleusercontent.com/8u19J1sdaNYF58O8szOyt_1f2an8_-kozTDQPXTAf1wmcRa8e8zkZPpoWFut00ln_QX-ISWIiNteEFqnd4LHeXUJmUBfHqayv6Gt1w_l3kzLqif-vaL4NqM5-_l-bIbZUPvwuBM" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">를 대입하면:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B1%7Dv_%7B1%7D%2Bm_%7B2%7Dv_%7B2%7D%3Dm_%7B1%7Du_%7B1%7D%2Bm_%7B2%7Du_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/YBbxIas9c1c_oBA5v5RWqT-pwxZKp5ORHUbXaoiR6LdCf8qg_UVHxnAdUsJqHOHK-s8l5TmjQ1MXyFfIlsVs-ZUUPnEQQtvic_FOoABgJy1xtzlLFBvRXsb166xkDlMN_NfItII" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">가 됩니다. 이 것이 운동량 보존 법칙입니다.</span></p><br><br><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:24px;font-family:Arial;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">문제</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">그럼 이 두 공식들을 사용하여 몇 가지 문제를 풀어보겠습니다.</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">8kg의 질량을 가진 구체와 1kg의 질량을 가진 물체가 각각 4m/s와 2m/s의 속도로 서로를 향해 충돌한다. 이 두 물체가 충돌한 후의 각각의 속도를 구하시오.</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">주어진 물리량:</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"> </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B1%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/hUZCUkt-j5_Q7IMUMXG48j354wW0afJtzoPNkMZ6kMEPkymgXufasKvIXua4ID7nNmcQBmrq3K0apUdLlvKHYP9amC4Hrvb0TKQS2RTAYqIE86mWmoCayGHyTuyNig89Hy453ik" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">= 8kg;  </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/BtEJjT0Y_EFGnkP0nv7lnq3Ge7neGGVzTnpSKZkYTohKWY2VBXgQxjwFbiIGEes3Qigpbocrnbuco6J6A7D6PxCRCHTQITF_u3lnpl5dsVjbYqlLvEkPkR5aKKOVdkLqxo6lKHs" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">= 1kg;  </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/P0tEHZlDKg1-ud-Ya58aVW04q1U9cOIMHuc94-2gJBZi_cBCI5Mo2-vHI7R8xAVs5YI2Y92GgW1MvrJiH4FAiZnkusOF5SXjZ5K96tnn5gv5Y6Cf0-2J0VKf29zmuOSo7a_ReXw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">= 4m/s;  </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B2%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/32r_977XuFWa3czJaSI2ZXI-xOSuyNLfRxEA6WRAsfpE94LFq6MhLqRMo-CM_EQBZnLwxsCpsYOkd18qYWgU7IbtVc7Xyrn3U5nNCes4ewGtnzNc5Mp-Y_T5SUNqD8JsZL-mgQM" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">= 2m/s</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">구할 물리량: </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bu_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/NqZm_wxi6j5nxN_TgtiVr4cmHYXNePVWoig7UaiDTz2Dd00hs-z81-m16mDGiWu84ykX7D1v3ECZ-Rf9GO6hqXQnlPvjjHSWnnuIfrkzMpZ_6-Tjvr9unAxaPYM8VgUVPHqt63s" style="border:none;" alt=""></span></a><span style="font-size:14.6666666666667px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">; </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bu_%7B2%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/8WnUZQFAb_Ya_YZh4F-kfJAlcEwUNLEuQ9L8_XaS137PxWIvW0fuRl_wIJJPOg7B5WTY4RE7VeIaS2wOEWiacyzkosSH75s3decn7R4NcRAoKPzaYE7CwJ7revd6vnZExSUac90" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">공식:</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"> </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cfrac%7B1%7D%7B2%7D*m_%7B1%7D*v_%7B1%7D%5E%7B2%7D%2B%5Cfrac%7B1%7D%7B2%7D*m_%7B2%7D*v_%7B2%7D%5E%7B2%7D%3D%5Cfrac%7B1%7D%7B2%7D*m_%7B1%7D*u_%7B1%7D%5E%7B2%7D%2B%5Cfrac%7B1%7D%7B2%7D*m_%7B2%7D*u_%7B2%7D%5E%7B2" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/GkHXIP8cVuDCEG_O_iaNKZ96_pOc7SOhoIGJmP_1TQC-WjU5wzxUOWIIHPfQcbV3GWyRJXoenS8h7HR_2HBNU8YxDobHN2bg8IcU0j_yfm_McD10pvDe86Ace6MQTUf6JTPcRk0" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><span class="Apple-tab-span" style="white-space:pre;"> </span></span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B1%7Dv_%7B1%7D%2Bm_%7B2%7Dv_%7B2%7D%3Dm_%7B1%7Du_%7B1%7D%2Bm_%7B2%7Du_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/YBbxIas9c1c_oBA5v5RWqT-pwxZKp5ORHUbXaoiR6LdCf8qg_UVHxnAdUsJqHOHK-s8l5TmjQ1MXyFfIlsVs-ZUUPnEQQtvic_FOoABgJy1xtzlLFBvRXsb166xkDlMN_NfItII" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;font-weight:bold;vertical-align:baseline;white-space:pre-wrap;">문제 풀이:</span><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"> </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">운동량 보존 법칙: </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_%7B1%7Dv_%7B1%7D%2Bm_%7B2%7Dv_%7B2%7D%3Dm_%7B1%7Du_%7B1%7D%2Bm_%7B2%7Du_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/YBbxIas9c1c_oBA5v5RWqT-pwxZKp5ORHUbXaoiR6LdCf8qg_UVHxnAdUsJqHOHK-s8l5TmjQ1MXyFfIlsVs-ZUUPnEQQtvic_FOoABgJy1xtzlLFBvRXsb166xkDlMN_NfItII" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 식에 주어진 물리량들을 각각 대입합니다. 대입하면:</span></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=8kg*4m%2Fs%2B1kg*(-2m%2Fs)%3D8kg*u_%7B1%7D%2B1kg*u_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/-c-pyfPFqvkpTzlOE9ROJKkKv08sahl6bXa2A-60etxCb9a5pb7y9GOILd18Pdl0PhzQww0sGCjfe_01Rkv7jjF6rMpjziMmt5SGMNpyDg3t8RGkDgugWbL4m7q6gsc8Fyod630" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">            </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">       </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=32kg*m%2Fs%20-2kg*m%2Fs%3D8kg*u_%7B1%7D%2B1kg*u_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/CcQgX4rnC2RjheInO8fOsjx0NBG8XkxIbkJw_EmH3q3q11x6n9AA5_8X_jOyc0W39jzr9zkf_zKYFSXUsgMLUYLW2JlGRmbj4ABGSKqp2IPFxGm-8F5i032bsqXcudv6TSC4hFQ" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">                                           </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">                              </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=30kg*m%2Fs%3D8kg*u_%7B1%7D%2B1kg*u_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/3cSnt3wo-fr4ylx4RslDoWZ1_6CXrNRe3PLN9MgA1jyZuOKp3qRejKQBQqIjnA4MSFdf00Mkyzh5QMNGqmrIOt7QXSrogsdA23_Pe9YvueMhQGfGpxhZ9nPIrydX_o1aCuNrHAo" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">                                </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cmid%5Cdiv%20kg" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/eFzc5OqSSqcFGiJ0SOv3Akl0KhImtEZrycKwsbgUrKeNXvjmIkFtEzQvevPh787VLh35bJ77KbQtamIXUbRuCNy0hh4R7QHxz0iOXVnIbf-vz0OTbk7T5ZsRYLLtehgmLxjZXfc" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">                                     </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=30m%2Fs%3D8u_%7B1%7D%2Bu_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/2fFpmYok7AtzREcBUJRSsPpAT7pPLZmXWwwxfUaIDsOXsA7GmqnKUSe9UIKwewa5Pd_ap2-InSQ_6DqUjNillbDtM67qqf3yCL-0BztF--GMqqvqR6riCKsbWz3nNQpR6fgljjQ" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">                                                 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cmid-8u_%7B1%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/jBF4FzKB3FD5ls-Twc1nfj_QH3XfFHc2NAWpq0c-1QdwdPKMhJ14ouM2UZ53zT5GZFjnIdYZ9kTYIFRfpm3UnUTXAAxBgKdctS0EanUdx4SQbYP1R81ZYpPU-InZTNCZb_zOceM" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">                                </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=30%5Cfrac%7Bm%7D%7Bs%7D-8u_%7B1%7D%3Du_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/Ea3sy3BYhdXVVfv9MjUP5lgfQTQURoIrJ1JeJ-Ja68IR5aqeyqdnng-ZErge2leDCNkR7imcbseihR75e4O7_lifb5wprfLTs23TiuB1k0H0N-G-czgwBlSca7T52o1FmKIao5k" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">에너지 보존 법칙:</span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cfrac%7B1%7D%7B2%7D*m_%7B1%7D*v_%7B1%7D%5E%7B2%7D%2B%5Cfrac%7B1%7D%7B2%7D*m_%7B2%7D*v_%7B2%7D%5E%7B2%7D%3D%5Cfrac%7B1%7D%7B2%7D*m_%7B1%7D*u_%7B1%7D%5E%7B2%7D%2B%5Cfrac%7B1%7D%7B2%7D*m_%7B2%7D*u_%7B2%7D%5E%7B2" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/GkHXIP8cVuDCEG_O_iaNKZ96_pOc7SOhoIGJmP_1TQC-WjU5wzxUOWIIHPfQcbV3GWyRJXoenS8h7HR_2HBNU8YxDobHN2bg8IcU0j_yfm_McD10pvDe86Ace6MQTUf6JTPcRk0" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 식에도 마찬가지로 주어진 물리량들을 대입합니다:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=0.5*8kg*(4%5Cfrac%7Bm%7D%7Bs%7D)%5E%7B2%7D%2B0.5*1kg*(-2%5Cfrac%7Bm%7D%7Bs%7D)%5E%7B2%7D%3D0.5*8kg*u_%7B1%7D%5E%7B2%7D%2B0.5*1kg*u_%7B2%7D%5E%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh3.googleusercontent.com/ShipSzmGyX7oYqhoFmv1LKo12Jxmb6t19DypKXbHu8-l4b1_GvJWpqGIQrM6iA1LeIXJDO0HftmYO02wByqGlb5tNXBlgas0CivnnediTnrmh5rbLIFU64U9aoOwFTDAs0wiRmM" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 식을 정리하고, kg으로 나누고, 다시 2를 곱하면:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=132%5Cfrac%7Bm%5E%7B2%7D%7D%7Bs%5E%7B2%7D%7D%3D8u%5E%7B2%7D_%7B1%7D%2Bu%5E%7B2%7D_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/IYG2Tgd4ekZbKzcKuCpOj-sJjcHN3rcL7gtjTFJS90Ly7RLcsDFGMesERWWUz2hP6nir7gGPBesf2pWOF5h1xWcjbz24JndPzo3gPKckWgqqQSYQ-iryHb4h10P5cMB-6ieXtsw" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 식에 아까 구한 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=30%5Cfrac%7Bm%7D%7Bs%7D-8u_%7B1%7D%3Du_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/Ea3sy3BYhdXVVfv9MjUP5lgfQTQURoIrJ1JeJ-Ja68IR5aqeyqdnng-ZErge2leDCNkR7imcbseihR75e4O7_lifb5wprfLTs23TiuB1k0H0N-G-czgwBlSca7T52o1FmKIao5k" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">를 대입합니다:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=132%5Cfrac%7Bm%5E%7B2%7D%7D%7Bs%5E%7B2%7D%7D%3D8u%5E%7B2%7D_%7B1%7D%2B(30%5Cfrac%7Bm%7D%7Bs%7D-8u_%7B1%7D)%5E%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/laPbxfoRDTnunV6bvYMW8Sli795lseyhix7AneR5XjY9Wxy4u3LUiWoXE-VXtColo-ZJS1kbtVD0qa_fverg9NLn3brlBqEI3TEhnjAOAYRSsAD3mt1b5YE2dnY3arhVVMlRgEY" style="border:none;" alt=""></span></a></p><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 식을 전개하고, 한 변으로 모으면:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=0%3Du%5E%7B2%7D_%7B1%7D-%5Cfrac%7B20%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7Du_1%2B%5Cfrac%7B32%7D%7B3%7D%5Cfrac%7Bm%5E2%7D%7Bs%5E2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh3.googleusercontent.com/7-6BPPcv__Ktq-baPFuzInOeU_HdCToZvY5geKDcbM171DkQrMHwDnZTMrACPL43m8cJEJ98iO8_F3ZALaJsydsQept1oNKJ_bXrww3LjhOqkNuQWvvJXBh4gM8qO6Gg-1d8PsY" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이차 방정식이 됩니다. 이 식을 근의 공식으로 풀면:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_1_%7B1%7D%3D%5Cfrac%7B12%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/iZvl54mhcTHTFjv5a4e0Z8VxfbJbB5DQv_U4_MfOhFILLljqS9sTCRPF1SAva8dlvaxF3FHSAggPlPyPYNsFKEOkjTeaKLYXcz2TLTGN7isdOCRiykpg2XMH2iaE7e3OLFw5C4U" style="border:none;" alt=""></span></a><span style="font-size:14.6666666666667px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">와 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_1_%7B2%7D%3D%5Cfrac%7B8%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/Y1QpFmB1nn8Wi8i5V7L-9ed61T5K2-0H5TuwCD6_c8r3d7-wINrbnynUmluy29b6vga5wLik4b5HPCcKbE8OGEgLoxW_DoRhrWJ542B9pV5GB38rcT06lZKLn90_dqS-r9NBBX4" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">의 두 개의 값을 얻게 됩니다.</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">그리고 이 두 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bu_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/NqZm_wxi6j5nxN_TgtiVr4cmHYXNePVWoig7UaiDTz2Dd00hs-z81-m16mDGiWu84ykX7D1v3ECZ-Rf9GO6hqXQnlPvjjHSWnnuIfrkzMpZ_6-Tjvr9unAxaPYM8VgUVPHqt63s" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">들을 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=30%5Cfrac%7Bm%7D%7Bs%7D-8u_%7B1%7D%3Du_%7B2%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/Ea3sy3BYhdXVVfv9MjUP5lgfQTQURoIrJ1JeJ-Ja68IR5aqeyqdnng-ZErge2leDCNkR7imcbseihR75e4O7_lifb5wprfLTs23TiuB1k0H0N-G-czgwBlSca7T52o1FmKIao5k" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">에 대입하면 당연히 두 개의 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bu_%7B2%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/8WnUZQFAb_Ya_YZh4F-kfJAlcEwUNLEuQ9L8_XaS137PxWIvW0fuRl_wIJJPOg7B5WTY4RE7VeIaS2wOEWiacyzkosSH75s3decn7R4NcRAoKPzaYE7CwJ7revd6vnZExSUac90" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">를 얻게 됩니다:</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_2_%7B1%7D%3D-2%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/9Q4drVj4sSj10f6eMDkWYfm0nwYfYeaWyIzjUITkJGsJ_utM8VyBqHVvRdwveiLI7Aox3wmS-0bsGnLNz_K547-qa36KIKiNK1nW3lPSNBtMygagZfbjtnaBluSHjMPfcRAp_-Y" style="border:none;" alt=""></span></a><span style="font-size:14.6666666666667px;font-family:Arial;vertical-align:baseline;white-space:pre-wrap;background-color:transparent;">; </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_2_%7B2%7D%3D%5Cfrac%7B26%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh3.googleusercontent.com/bKh9-eyKZaXeuOw1uzKqkj5I1W0zOqrKHvdyqzpRT5_eSBCAy5EGE3gJq-t73NxdX-GcHHbItKVlPv8XDATy26a1f5tiBB_o82YOKYr5mTC6fplAgpHe7uLQ_-6NOuShtnJH6dI" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">뭔가 이상합니다. 분명 두 물체가 충돌한 후 의 속도는 각각 하나 일수 밖에 없습니다. 그런데 왜 두 개의 값이 나왔을까요? </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">그것은 우리가 충돌 후 속도 u를 구하기 위해 2차 방정식을 사용했기 때문입니다. 2차 방정식의 해는 최대 2개 이지요. 즉, 이 두 개의 값은 수학적으로는 둘 다 맞으나 물리적으로는 오직 둘 중 한개만 맞는 값입니다.  </span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">그렇다면 도대체 어떻게 둘 중 맞는 값을 찾아낼까요? 우선 첫 번째 값들을 봅시다.</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_1_%7B1%7D%3D%5Cfrac%7B12%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/iZvl54mhcTHTFjv5a4e0Z8VxfbJbB5DQv_U4_MfOhFILLljqS9sTCRPF1SAva8dlvaxF3FHSAggPlPyPYNsFKEOkjTeaKLYXcz2TLTGN7isdOCRiykpg2XMH2iaE7e3OLFw5C4U" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">; </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_2_%7B1%7D%3D-2%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/9Q4drVj4sSj10f6eMDkWYfm0nwYfYeaWyIzjUITkJGsJ_utM8VyBqHVvRdwveiLI7Aox3wmS-0bsGnLNz_K547-qa36KIKiNK1nW3lPSNBtMygagZfbjtnaBluSHjMPfcRAp_-Y" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">보시면 알다시피 두 물체의 충돌 한 후의 속도가 충돌 전의 속도와 같습니다. ( </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/P0tEHZlDKg1-ud-Ya58aVW04q1U9cOIMHuc94-2gJBZi_cBCI5Mo2-vHI7R8xAVs5YI2Y92GgW1MvrJiH4FAiZnkusOF5SXjZ5K96tnn5gv5Y6Cf0-2J0VKf29zmuOSo7a_ReXw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">= 4m/s;  </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B2%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/32r_977XuFWa3czJaSI2ZXI-xOSuyNLfRxEA6WRAsfpE94LFq6MhLqRMo-CM_EQBZnLwxsCpsYOkd18qYWgU7IbtVc7Xyrn3U5nNCes4ewGtnzNc5Mp-Y_T5SUNqD8JsZL-mgQM" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">= 2m/s). 충돌 전의 속도와 충돌 후의 속도가 같은 경우가 아예 불가능하지는 않습니다. 그러한 경우도 있지요. 하지만 지금 같은 경우는 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_1" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/-gy2ip2th_vcrx5KwcdJgVmVQQSIlQkE3nt39Itz2E02jsN35pLKV3bVXiMbrwfX-quAyhs-f-ULizQQXXFuDU7LJerguL6CcNIfmb1aT-yiyME9tYfoJNCyCeBwjWDUNVpu1sw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_2" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/448E-Ay38cFXjV3EbKvt47w8XfGpGwvFWlPwndruVqkMfNOaMbIZ7Paf1zAq8uQGNOg4Jdhj77RFAUhkx11Xg8OA1X1vOKxxuxTrxNuoX2PtGOHfRB92aq9F6vdp7VgvCbyobgk" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">보다 무려 8배나 크고 속도도 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=%5Cstackrel%7B%5Crightarrow%7D%7Bv_%7B1%7D%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh4.googleusercontent.com/P0tEHZlDKg1-ud-Ya58aVW04q1U9cOIMHuc94-2gJBZi_cBCI5Mo2-vHI7R8xAVs5YI2Y92GgW1MvrJiH4FAiZnkusOF5SXjZ5K96tnn5gv5Y6Cf0-2J0VKf29zmuOSo7a_ReXw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">가 더 큽니다. 즉, </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_1" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/-gy2ip2th_vcrx5KwcdJgVmVQQSIlQkE3nt39Itz2E02jsN35pLKV3bVXiMbrwfX-quAyhs-f-ULizQQXXFuDU7LJerguL6CcNIfmb1aT-yiyME9tYfoJNCyCeBwjWDUNVpu1sw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 가진 운동 에너지가 더 크지요. 그러므로 우리는 두 물체가 충돌 후 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_1" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/-gy2ip2th_vcrx5KwcdJgVmVQQSIlQkE3nt39Itz2E02jsN35pLKV3bVXiMbrwfX-quAyhs-f-ULizQQXXFuDU7LJerguL6CcNIfmb1aT-yiyME9tYfoJNCyCeBwjWDUNVpu1sw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">이 가던 방향으로 운동할 것이라는 것을 짐작할 수 있습니다. </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_1" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/-gy2ip2th_vcrx5KwcdJgVmVQQSIlQkE3nt39Itz2E02jsN35pLKV3bVXiMbrwfX-quAyhs-f-ULizQQXXFuDU7LJerguL6CcNIfmb1aT-yiyME9tYfoJNCyCeBwjWDUNVpu1sw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">의 속도는 충돌 때문에 조금 줄어들고 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_2" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/448E-Ay38cFXjV3EbKvt47w8XfGpGwvFWlPwndruVqkMfNOaMbIZ7Paf1zAq8uQGNOg4Jdhj77RFAUhkx11Xg8OA1X1vOKxxuxTrxNuoX2PtGOHfRB92aq9F6vdp7VgvCbyobgk" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">의 속도는 -부호가 +부호로 바뀌며 방향을 바꾸겠지요. 그리고 이 생각을 두 번째 값들은 잘 대변합니다.</span></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_1_%7B2%7D%3D%5Cfrac%7B8%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh6.googleusercontent.com/Y1QpFmB1nn8Wi8i5V7L-9ed61T5K2-0H5TuwCD6_c8r3d7-wINrbnynUmluy29b6vga5wLik4b5HPCcKbE8OGEgLoxW_DoRhrWJ542B9pV5GB38rcT06lZKLn90_dqS-r9NBBX4" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">; </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_2_%7B2%7D%3D%5Cfrac%7B26%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh3.googleusercontent.com/bKh9-eyKZaXeuOw1uzKqkj5I1W0zOqrKHvdyqzpRT5_eSBCAy5EGE3gJq-t73NxdX-GcHHbItKVlPv8XDATy26a1f5tiBB_o82YOKYr5mTC6fplAgpHe7uLQ_-6NOuShtnJH6dI" style="border:none;" alt=""></span></a></p> <p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_1" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/-gy2ip2th_vcrx5KwcdJgVmVQQSIlQkE3nt39Itz2E02jsN35pLKV3bVXiMbrwfX-quAyhs-f-ULizQQXXFuDU7LJerguL6CcNIfmb1aT-yiyME9tYfoJNCyCeBwjWDUNVpu1sw" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">의 속도는 충돌 후 조금 감소했고, </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=m_2" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/448E-Ay38cFXjV3EbKvt47w8XfGpGwvFWlPwndruVqkMfNOaMbIZ7Paf1zAq8uQGNOg4Jdhj77RFAUhkx11Xg8OA1X1vOKxxuxTrxNuoX2PtGOHfRB92aq9F6vdp7VgvCbyobgk" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">의 속도는 충돌 후 부호가 바뀌어 반대 방향으로 가고 있습니다. 따라서 답은 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_1%3D%5Cfrac%7B8%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/bLtgZZm_ejipQcpNc8MrGaFs1R6mg13Bz82ce7reli0r9edV5aQRLsoqH114SvPmyU5GULYM3a9SmobslZSnuJfDS_jSodJRd8Es3YkWSuuRjjzP4E34AxBWRD0dFXvk-BAwfj8" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">과 </span><a target="_blank" href="http://chart.googleapis.com/chart?cht=tx&chl=u_2%3D%5Cfrac%7B26%7D%7B3%7D%5Cfrac%7Bm%7D%7Bs%7D" style="text-decoration:none;" target="_blank"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><img src="https://lh5.googleusercontent.com/IAEAI0l-bd29dxWS5Ec_1CpZzApyliF8lPdIcveYlokWfgXnX0ErE2Xb4stV4ZKEdEYkLlMREPG8F-3V1DwPtl22Bed2Vvz1Oy3mDykDcRGW7lA43TDC04t0eOEQxKZ-e4B8sLs" style="border:none;" alt=""></span></a><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">입니다.</span></p><br><br><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;">여기까지 가 이 시리즈의 파일럿-에너지 보존법칙, 운동량 보존 법칙 이었습니다. 시간과 힘이 남아 있다면 조만간 다시 글을 올리겠습니다. 긴 글 봐주셔서 감사합니다. </span></p> <div><span style="font-size:16px;font-family:Arial;color:#252525;vertical-align:baseline;white-space:pre-wrap;"><br></span></div>