题目内容
如图所示,在水平向左的匀强电场中,一根不可伸长的绝缘细线一端拴一个质量为m电荷量为q的带负电小球,另一端固定在O点。把小球拉到使细线水平的位置A然后将小球由静止释放,小球沿弧线运动到细线与水平成θ=600的位置B时速度为零,则电场强度E=_______,球在B点时,细线拉力为T=__________.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241302168892117.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241302168892117.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130216905776.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130216951631.png)
带电小球从A运动到B过程中,重力做正功,电场力做负功,根据动能定理可得
,所以
,在B点时拉力![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130217061970.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241302169831175.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130216905776.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130217061970.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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