如图所示，质量为m的小球A以水平速率v与静止在光滑水平面上质量为3m的
小球B正碰后，小球A的速率为v2.则碰后B球的速度为(以v方向为正方向)（ ）
A．
B．-v
C．-
D．
答案：D
系统碰撞过程动量守恒：以A球运动方向为正.
mv=mv′+3mv″ ①
由题意知：v′=
或v′=-
代入①式得：v″=
或v″=
v″<v′不合理.故将v″=舍去，D正确.
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| Some one says," time is money." But I think time is 1 important than money. Why? Because when money is spent, we can get it back. however, when time is 2 , It'll never return. That is 3 we must't waste time. It goes without saying that time is usually limited. Even a second is very important. we should make full use of our time to do 4 useful. But it is a pity that there are a lot of people who don't know the important of time. They 5 their limited time smoking, drinking and playing cards. They don't know that wasting time means wasting part of their own 6 . In a word, we should save time. we shouldn't leave today's work for tomorrow, Remember: we have no time to lose. | |||
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