题目内容
(15分)一匀强电场,场强方向水平向左,如题7图所示.一个质量为
的带正电的小球,从
点出发,初速度的大小为
,在静电力与重力的作用下,恰能沿与场强的反方向成
角的直线运动.求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029235181600.png)
(1)小球运动的加速度大小.
(2)小球从
点运动到最高点的过程中电势能的变化.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923456346.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923471300.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923487326.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923487302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029235181600.png)
(1)小球运动的加速度大小.
(2)小球从
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923471300.png)
(1)
(2) ![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029235651060.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923549641.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029235651060.png)
试题分析:(1)设小球的电荷量为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923596314.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923612420.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923627416.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029236432481.png)
有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923659773.png)
由此可知,小球做匀减速直线运动的加速度大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029236741191.png)
(2)设从O点到最高点的位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923690260.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923705585.png)
运动的水平距离为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002923721563.png)
由以上各式可得静电力做功
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029237371238.png)
电势能的变化
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250029237521234.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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