题目内容
(8分)真空中有一固定的点电荷B,将一带电小球A(可看成质点)从B的正上方距电荷B为L处无初速释放时,小球A的加速度大小为
,方向竖直向下。求:当小球A向下运动
时,它的加速度多大?球A在向电荷B运动的过程中,与B相距多远时速度最大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934275390.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934447372.png)
设带电小球A的质量为m,当小球A的加速度大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934275390.png)
mg-
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934587708.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934275390.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241319347591012.png)
设当小球A向下运动
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934447372.png)
mg-
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241319348211080.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934852322.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934884379.png)
设球A在向电荷B运动的过程中,与B相距为r时速度最大,此时重力等于库仑力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934962168.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131934993707.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131935024628.png)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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