题目内容
真空中存在空间范围足够大的,水平向右的匀强电场。在电场中,若将一个质量为
,带正电的小球由静止释放,运动中小球的速度与竖直方向夹角为
(取
,
),现将该小球从电场中某点以初速度
竖直向上抛出,则在此运动过程中( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134152976337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153007391.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153054658.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153116664.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153272325.png)
A.小球受到的电场力大小为![]() |
B.小球到达最高点时的动能为![]() |
C.小球从抛出点到与抛出点同一水平高度处电势变化量为![]() |
D.小球的最小动量为![]() |
CD
小球由静止释放,则在合力方向上做匀加速运动,有
;电场力大小为
,A错误;运动到竖直方向的时间为
,到达最高点时的动能为
,B错误;当小球从抛出点到与抛出点同一水平高度处时时间为
,电场力做功为:
,则电势变化量为
,C正确;根据冲量等于动量的变化量,当速度方向与合力方向夹角大于90°时动量减小,当夹角小于90°时动量增加,故小球的速度方向与电场方向夹角为370斜向上时,动量最小,此时速度大小为:
,最小动量为:
,D正确。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153678919.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153787584.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153818524.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241341538811328.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153943591.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241341540841495.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153584667.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134154380649.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134153631596.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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