满载砂子的总质量为M的小车，在光滑水平面上做匀速运动，速度为v0．在行驶途中有质量为m的砂子从车上漏掉，则砂子漏掉后小车的速度应为：（ ）
A．v0
B．Mv0 M-m
C．mv0 M-m
D．(M-m)v0 M
设漏掉质量为m的沙子后，砂子从车上漏掉的瞬间由于惯性速度仍然为v0，汽车速度为v′，根据水平方向动量守恒可得：
Mv0=mv0+（M-m）v′
解得：v′=v0，故BCD错误，A正确．
故选A．
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| I had a summer camp with my classmates last year. Early in the morning, we 1 at the bus station. After saying 2 to our parents, we got on the bus. It 3 us more than two hours to arrive at the campground. It was the first time for us to he away from our 4 , so some of us started to feel homesick (想家的) 5 , when the evening party began, we felt happy again. The next day, everybody went to the boating class. At first, my friend and I worked hard, but the 6 wouldn't listen to us. Then the teacher taught us 7 to work together (共同). After many tries, we did much 8 . The swimming class was my favorite. It was 9 to stay in the cool water. The swimming teacher was a fury man, and he often made us 10 happily. I learned a lot of new things during the summer camp. I also learned how to look after myself. | ||||
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