小勇用如图所示滑轮组拉着物体匀速前进了0.2m,则绳子自由端移动的距离为多少?若不计滑轮重、绳重和摩擦,物体与地面的摩擦力为9N,则他所做的功是多少?如果小勇对绳的拉力F=4N,该
2023-04-27
问题描述:
小勇用如图所示滑轮组拉着物体匀速前进了0.2m,则绳子自由端移动的距离为多少?若不计滑轮重、绳重和摩擦,物体与地面的摩擦力为9N,则他所做的功是多少?如果小勇对绳的拉力F=4N,该滑轮组的机械效率为多少?![](https://img1.runjiapp.com/duoteimg/tiku/imgs/203fb80e7bec54e7b5c8d5afba389b504fc26a5f.png)
最佳答案:
(1)从图中可知,n=3,则s=3s′=3×0.2m=0.6m;(2)F=13f=13×9N=3N,W=Fs=3N×0.6m=1.8J;(3)W有=fs′=9N×0.2m=1.8J,W总=F′s=4N×0.6=2.4J,η=W有W总×100%=1.8J2.4J×100%=75%.答:绳子自由端移动的距离...
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