题目内容
如右图所示,
为两个固定点电荷,其中
带正电,它们连线的延长线上有a、b两点.一正试探电荷以一定的初速度沿直线从b点开始经a点向远处运动,其速度图象如下图所示.则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242200057491445.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242200057801878.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824220003721486.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824220004672362.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242200057491445.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242200057801878.jpg)
A.![]() |
B.![]() |
C.试探电荷从b到a的过程中机械能增大 |
D.试探电荷从b到a的过程中电势能减小 |
B
试题分析:根据速度图象的斜率等于加速度,由图知,试探电荷经过a点时的加速度为零,由牛顿第二定律得知,电荷所受的电场力为零,a点的合场强必为零,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824220003721486.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824220005795383.png)
故选B
点评:本题的解题之处在于确定出电荷在a点的加速度为零,根据能量守恒判断电势能的变化,判断电势能和机械能的变化
![](http://thumb2018.1010pic.com/images/loading.gif)
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