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工人师傅用如图12-Z-20所示的滑轮组,在10s内把900N的货物匀速提高2m,在此过程中,拉力所做的功是2400J.求:(1)拉力F移动的距离.(2)工人师傅所做有用功的功率.(3)滑轮组的机械...
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