题目内容
如图所示,一根轻质细杆的两端分别固定着A、B两只质量均为m的小球,O点是一光滑水平轴,已知
,
使细杆从水平位置由静止开始转动,当B球转到O点正下方时,求:(1)物体
对细杆的拉力。(2)杆对B球做功
。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241939298621655.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193927787483.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193928287537.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193928848309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193929269396.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241939298621655.jpg)
(1)
,方向竖直向下(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193930783827.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193930049688.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193930783827.png)
试题分析:(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193931297396.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241939319061113.png)
且
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193932811520.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193933497776.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193933918817.png)
在最低点,对
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193928848309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193935041871.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193935743681.png)
根据牛顿第三定律,物体
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193928848309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193930049688.png)
(2)对
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193928848309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241939376311118.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193930783827.png)
点评:本题难度中等,应先判断系统机械能是否守恒,确定初末状态的动能和势能,规定零势能面应用机械能守恒定理公式求解
![](http://thumb2018.1010pic.com/images/loading.gif)
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