题干

如图所示,质量分别为m和2m的A、B两个木块间用轻弹簧相连,放在光滑水平面上,A靠紧竖直墙.用水平力F将B向左压,使弹簧被压缩一定长度,静止后弹簧储存的弹性势能为E.这时突然撤去F,关于A、B和弹簧组成的系统,下列说法中正确的是(   )

A:撤去F后,系统动量守恒,机械能守恒

B:撤去F后,A离开竖直墙前,系统动量不守恒,机械能守恒

C:撤去F后,A离开竖直墙后,弹簧的弹性势能最大值为 E3

D:撤去F后,A离开竖直墙后,弹簧的弹性势能最大值为E

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B,C

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    A thick book of rules and guidelines tells Hollywood moviemakers how to treat animals. Karen Rosa leads the American Humane Society's film and television group. He said, “Everything from the smallest insect to the largest mammal shall be protected. We believe that for the sake of entertainment, everybody should go home alive.

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    A new film “Rise of the Planet of the Apes” tells about the creation of super intelligent apes through science. However, no real animals were among the performers. Computer generated imagery provided the chimpanzees, gorillas and orangutans that movie goers see. Clare Richardson is the president of the Diane Fossey Gorilla Fund. She says computer generated imagery should decrease the use of animals in the film industry. She praises movie makers for the use of computer-made animals.