题目内容
质量均为m的三个带电小球A、B、C放置在光滑绝缘的水平面上,相邻球间的距离均为L,A球带电量qA=+10q;B球带电量qB=+q.若在C球上加一个水平向右的恒力F,如图所示,要使三球能始终保持L的间距向右运动,则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250007464231691.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746423590.png)
(1)C球带电性质是什么?
(2)外力F为多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250007464231691.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746423590.png)
(1)C球带电性质是什么?
(2)外力F为多大?
(1)C球带负电荷;(2)70k![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746438485.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746438485.png)
试题分析:(1)由于A、B两球都带正电,它们互相排斥,C球必须对A、B都吸引,才能保证系统向右加速运动,故C球带负电荷.
(2)以三球为整体,设系统加速度为a,则F=3ma ①
隔离A、B,由牛顿第二定律可知:
对A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746454715.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746470669.png)
对B:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746470669.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746501675.png)
联立①、②、③得:F=70k
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000746438485.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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