题目内容
如图9所示中滑块和小球的质量均为m,滑块可在水平放置的光滑固定导轨上自由滑动,小球与滑块上的悬点O由一不可伸长的轻绳相连,轻绳长为l。开始时,轻绳处于水平拉直状态,小球和滑块均静止。现将小球由静止释放,当小球到达最低点时,测得滑块对导轨的压力为3mg。求小球从释放到第一次到达最低点的过程中,绳的拉力对小球做功的大小。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153478111936.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153478111936.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347826440.gif)
由滑块对导轨的压力为3mg可知:此时细绳对小球的的拉力2mg,则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347826618.gif)
滑块与小球组成的系统在小球摆动过程中机械能守恒,故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347842828.gif)
对块滑由动能定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347873670.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347826618.gif)
滑块与小球组成的系统在小球摆动过程中机械能守恒,故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347842828.gif)
对块滑由动能定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115347873670.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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