题目内容
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241206560644709.jpg)
在场强为B的水平匀强磁场中,一质量为m、带正电q的小球在O静止释放,小球的运动曲线如图所示.已知此曲线在最低点的曲率半径为该点到z轴距离的2倍,重力加速度为g.求:
(1)小球运动到任意位置P(x,y)的速率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656064192.gif)
(2)小球在运动过程中第一次下降的最大距离ym.
(3)当在上述磁场中加一竖直向上场强为E(
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656080470.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656142214.gif)
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656158440.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656189584.gif)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656205682.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241206562202093.jpg)
⑴洛伦兹力不做功,由动能定理得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656236539.gif)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656158440.gif)
⑵设在最大距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656267216.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656142214.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656298589.gif)
且由②知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656314484.gif)
由③④及
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656330401.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656189584.gif)
⑶小球运动如图所示,由动能定理得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656376784.gif)
由圆周运动得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656392750.gif)
且由⑥⑦及
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656408446.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120656205682.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目