题目内容
如图所示,光滑绝缘细杆竖直放置,它与以正点电荷Q为圆心的某一圆周交于B、C两点,质量为m,带电量为-q的有孔小球从杆上A点无初速下滑,已知Q,且AB=h=BC,小球滑到B点时速度大小为
,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241930366842556.png)
(1)小球从A到B过程中电场力做的功.
(2)A、C两点电势差.
(3) 小球滑到C点时速度大小为多少
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193036107487.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241930366842556.png)
(1)小球从A到B过程中电场力做的功.
(2)A、C两点电势差.
(3) 小球滑到C点时速度大小为多少
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193037433632.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193038057667.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193038556517.png)
试题分析:此题考查电场能的性质,涉及到点电荷形成的电场电势的特点、非匀强电场中电场力做功的计算、电势差的计算以及动能定理的应用.
(1)设小球由A到B电场力所做的功为WAB,由动能定理得
mgh+WAB=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193039321694.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193037433632.png)
(2)由于B、C在以Q为圆心的圆周上,所以UB=UC,
∵WAB=WAC
∴WAC=qUAC UAC=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193038057667.png)
(3)mgh=mvc2/2-mvb2/2
点评:本题难度较小,首先应进行受力分析,在进行做功分析,确定初末状态,根据动能定理列公式求解
![](http://thumb2018.1010pic.com/images/loading.gif)
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