题干

如图所示,重为100N的物体B,在足够深的水中匀速下沉,通过滑轮组拉着重600N的物体A沿水平方向匀速运动,在4s内物体A移动了0.8米,已知B的密度是水的密度的5倍,动滑轮重12N,不计绳重及滑轮与绳之间的摩擦,g取10N/kg(     )

A:B对绳的拉力是20N

B:B对绳的拉力的功率是16W

C:A物体受摩擦力为148N

D:滑轮组的机械效率为90%

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答案(点此获取答案解析)

C

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