题目内容
(12分)如图所示,质量
kg的小球,带有
C的正电荷,套在一根与水平方向成
角的足够长绝缘杆上。小球可以沿杆滑动,与杆间的动摩擦因数
,这个装置放在磁感应强度
T的匀强磁场中,求小球无初速释放后沿杆下滑的最大加速度和最大速度。(g=10m/s2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241312467874876.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246600572.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246662579.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246693491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246725449.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246756431.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241312467874876.jpg)
解:开始阶段小球速度小,洛伦兹力较小,杆对球支持力垂直杆斜向上,且逐渐减小,当速度达到某值后,支持力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246803411.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131246818992.png)
此后杆对球的支持力垂直于杆向下且随速度增大而增大,当摩托力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247037678.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241312470681073.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247037678.png)
且
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247115570.png)
由②③④解出:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247146753.png)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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