题目内容
如图所示,光滑绝缘水平桌面上固定一个光滑绝缘的挡板ABCD、AB段为直线,BCD段是半径为R的圆弧,挡板处在场强为E的匀强电场中,电场方向与圆环直径MN平行。现使一带电荷量为+q,质量为m的小球由静止从斜挡板内侧上某点释放,为使小球沿挡板内侧运动,从D点抛出,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022496964247.png)
(1)小球从释放点到N点沿电场强度方向的最小距离。
(2)在上问中小球经过N点时对挡板压力大小。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022496964247.png)
(1)小球从释放点到N点沿电场强度方向的最小距离。
(2)在上问中小球经过N点时对挡板压力大小。
(1)
(2)6qE
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002249711476.png)
试题分析:(1)小球经过M点时恰好无压力,此时对应的s最小,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002249727871.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022497421138.png)
由①②式解得s=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002249711476.png)
(2)过N点时,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002249789974.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002249805887.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002249820679.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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