题目内容
如图所示,一质量为m、电量为q的小球在电场强度E的匀强电场中,以初速度υ0沿直线ON做匀变速运动,直线ON与水平面的夹角为30°.若小球在初始位置的电势能为零,重力加速度为g,且mg=Eq,则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250028100424446.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250028100424446.png)
A.电场方向竖直向上 |
B.小球运动的加速度大小为g |
C.小球最大高度为![]() |
D.小球电势能的最大值为![]() |
BD
试题分析:以小球为研究对象进行受力分析如图所示:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250028101512932.png)
因小球所受电场力与重力大小相等,而合力方向只能与运动方向共线,所以可知电场力的方向只能如图所示,与水平方向成300夹角,所以选项A错误;故可知小球所受合力大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002810167511.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002810183647.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250028102451001.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250028102611562.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002810089566.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002810089566.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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