题目内容
如图所示,恒定的拉力大小F=8N,方向与水平线夹θ=60°角,拉着绳头使物体沿水平面移动
=2m的过程中,拉力做了多少功?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144424181322.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442402198.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144424181322.gif)
24J
如图所示,随着物体沿水平面前进
=2m,绳头从A点被拉到B点,由此可见:拉F所作用的物体(绳头)的位移S可由几何关系求得为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442449670.gif)
而力F与位移S间的夹角为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442465292.gif)
所以,这过程中拉F作用于绳头所做的功为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442496941.gif)
解法二 如图6-5绳子张力大小为F,但张力对物体做功包括沿F方向的张力所做的功W1和水平向右的张力所做的功W2,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442512993.gif)
解法三 如图6-6,绳子对物体拉力的合力大小为
,此合力做的功为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442558991.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082411444257410444.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442402198.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442449670.gif)
而力F与位移S间的夹角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442465292.gif)
所以,这过程中拉F作用于绳头所做的功为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442496941.gif)
解法二 如图6-5绳子张力大小为F,但张力对物体做功包括沿F方向的张力所做的功W1和水平向右的张力所做的功W2,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442512993.gif)
解法三 如图6-6,绳子对物体拉力的合力大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442527434.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114442558991.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082411444257410444.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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