Question

如图，动滑轮重20N，物体重80N，不计绳重和摩擦：

（1）请你在图中画出一种绕绳方法。

（2）根据你的绕绳方法，用滑轮组将物体匀速提升1m时，求作用在绳子上的拉力、有用功和滑轮组的机械效率。

　

Answer 1

解法一：

（1）绕绳方法如图······························································· 1分

（2）(80N+20N)=50N ··························· 1分

      W_有=G_物h=80N×1m=80J  ·········································· 1分

      W_总=FS=50N×2×1m=100J  ····································· 1分

      % ···························· 1分

（或J  ······························ 1分

 ···· 1分）

解法二：

（1）绕绳方法如第30题（b）图所示。  ······························· 1分

（2）解：···················· 1分

    ····································· 1分

  ······························· 1分

 ························· 1分

（或J ····························· 1分

     1分）