题目内容
如图所示,在一长为2l的不可伸长的轻杆的两端,各固定一质量为2m与m的A、B两小球,系统可绕过杆的中点O且垂直纸面的固定转轴转动.初始时轻杆处于水平状态,无初速释放后,轻杆转动.当轻杆转至竖直位置时,小球A的速率多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204361322951.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204361322951.jpg)
??![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120436163602.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120436163602.png)
??选初始位置为零势能面,A球、B球及地球为一系统,由机械能守恒定律,可得0=-2mgl+mgl+
(2m)v12+
mv22因为转轴在杆的中点O处,则v1=v2?联立解得v1=
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120436226338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120436226338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120436163602.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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