题目

使用如图所示的滑轮组，匀速提升一个质量为60kg的物体。若所用的拉力F为400N，物体提升高度为5m，求：(1)拉力F所做的功； (2)该滑轮组的机械效率。(g=10N/kg) 答案：【答案】(1) 4000J；(2) 75%【解析】(1)由图可知，承担动滑轮和货物得绳子段数n为2，则绳子自由端移动的距离为s=nh=2×5m=10m则拉力F所做的功为W=Fs=400N×10m=4000J(2)该滑轮组的机械效率为答：(1)拉力F所做的功为4000J；(2)该滑轮组的机械效率为75%。—Mr Wang bought a house with a large garden in Shanghai.—It be very expensive. I never even dream about itA. might B. can't C. must D. shouldn't