题目内容
如图所示,带电小球A、B的电荷量分别为QA、QB,OA=OB,都用长L的丝线悬挂在O点。静止时A、B相距为d。为使平衡时AB间距离减为d/2,可采用以下哪些方法
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241512262472103.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241512262472103.jpg)
A.将小球B的质量增加到原来的8倍 |
B.将小球A、B的质量都增加到原来的2倍 |
C.将小球A、B的电荷量都减小到原来的一半 |
D.将小球A、B的电荷量都减小到原来的一半,同时将小球B的质量增加到原来的2倍 |
AD
试题分析:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241512263101873.jpg)
如图所示,B受重力、绳子的拉力及库仑力;将拉力及库仑力合成,其合力应与重力大小相等方向相反;由几何关系可知,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151226528722.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151226731775.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241512268241180.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151226996844.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241512271361004.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151227261470.png)
点评:本题中B球处于动态平衡状态,注意本题采用了相似三角形法;对学生数学能力要求较高,应注意相应知识的积累应用.
![](http://thumb2018.1010pic.com/images/loading.gif)
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