问题
选择题
一个静止的质量为M的不稳定原子核，当它放射出质量为m、速度为v的粒子后，原子核剩余部分的速度为（ ）
A．-v
B．-mv (M-m)
C．-mv (m-M)
D．-mv M
答案
根据动量守恒定律研究整个原子核：
0=mv+（M-m）v′
v′=-mv (M-m)
故选B．
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一个静止的质量为M的不稳定原子核，当它放射出质量为m、速度为v的粒子后，原子核剩余部分的速度为（ ）
A．-v
B．-mv (M-m)
C．-mv (m-M)
D．-mv M
根据动量守恒定律研究整个原子核：
0=mv+（M-m）v′
v′=-mv (M-m)
故选B．
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| I know my brother better than anyone else in the world. Since the moment of his birth, I've been part of his life. I had spent seven 1 years in the world with the attention of those around me. But when Rohan was born, life 2 Suddenly I had to 3 my toys and there were no more bedtime stories or my own choice of food. Finally, I felt my 4 at my brother. The poor baby had no idea what had made me so unhappy. Maybe he found me strange, the only person in this house 5 did not like him. Whatever the reason was, he loved 6 me around. However, I seldom talked to him and 7 asked him to leave me alone. Then all that changed. I hardly remember everything of that day six years ago, 8 I do remember that I was feeling very angry. Somehow my feet led me to my brother's bed. My hand, completely 9 from my mind, reached through the bars (护栏). At once, he reached his small hand and softly touched 10 And that was all I needed. Through all the unhappiness of the day, that one moment changed 11 How could I hate someone who made me feel so important? For the 12 time, I saw my brother, not through the eyes of a child who was no longer favored (宠爱), but through the eyes of a 13 To this day, I can't imagine life 14 my brother. It is unbelievable how much I have 15 about life from a seven-year-old boy. Above all, Rohan has taught me that one should not care only for himself. | ||||
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