题目内容
如图,在竖直向下,场强为
的匀强电场中,长为
的绝缘轻杆可绕固定轴
在竖直面内无摩擦转动,两个小球A、B固定于杆的两端,A、B的质量分别为
和
(
),A带负电,电量为
,B带正电,电量为
。杆从静止开始由水平位置转到竖直位置,在此过程中电场力做功为 ,在竖直位置处两球的总动能为 。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241327553335870.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132754740318.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132754771280.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132754833292.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132754974362.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755161386.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755192476.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755255338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755301357.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241327553335870.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755395800.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241327554261204.png)
A B在转动过程中电场力对A B都做正功即:
,根据动能定理:
=
可求解在竖直位置处两球的总动能。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755473979.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241327555201286.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132755551480.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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