题目内容
如图所示,光滑绝缘细杆竖直放置,它与正电荷Q为圆心的某圆交于B,C两点,质量为m,带电荷量为-q的有孔小球从杆上A点无初速度下滑,已知q远小于Q,AB=h,BC=3h,小球滑到B点时速度大小为
,则:(1)小球到C时的速度大小为___ __;(2)A、C两点电势差___ __。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006362382360.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636223523.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006362382360.jpg)
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636285723.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636254519.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636285723.png)
试题分析::(1)因为杆是光滑的,所以小球从A到B过程中只有两个力做功:电场力的功WAB和重力的功mgh,由动能定理得
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006363011159.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636410926.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636425632.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006364411198.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636457649.png)
(2)因为B、C在同一个等势面上,所以φB=φC,即UAB=UAC由WAB=qUAB=qUAC得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006364721329.png)
故A、C两点电势差为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000636285723.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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