Question

如圖，動(dòng)滑輪重20N，物體重80N，不計(jì)繩重和摩擦：

（1）請你在圖中畫出一種繞繩方法。

（2）根據(jù)你的繞繩方法，用滑輪組將物體勻速提升1m時(shí)，求作用在繩子上的拉力、有用功和滑輪組的機(jī)械效率。

　

Answer 1

解法一：

（1）繞繩方法如圖······························································· 1分

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

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

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

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

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

 ···· 1分）

解法二：

（1）繞繩方法如第30題（b）圖所示。  ······························· 1分

（2）解：···················· 1分

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

  ······························· 1分

 ························· 1分

（或J ····························· 1分

     1分）