来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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  Because, what'll happen is,
  所以 将要发生的是
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  some energy will go into heating up the block;
  有一些能量将加热木块
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  it might even catch fire if the bullet's going too fast.
  假如子弹速度太大 木块甚至还会着火
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  But you can use the Law of Conservation of Momentum all the time
  但是任何时候你都可以使用动量守恒定律
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  in the first collision to deduce that M + m
  在第一个碰撞过程中来算出 M + m
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  times some intermediate velocity is the incoming momentum.
  乘以某个中间时刻的速度得到后面时刻的动量
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  You understand that?
  你们明白了吗
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  From that, you can find the
  从此 你可以求出
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  velocity v with which this composite thing,
  速度 v 当这个整体
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  block and bullet, will start moving.
  木块和子弹开始移动时
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  Once they start moving,
  一旦它们开始移动
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  it's like a pendulum
  它们就成为了一个摆