题目内容
如图所示,在y>0的空间中,存在沿y轴正方向的匀强电场E;在y<0的空间中,存在沿y轴负方向的匀强电场,场强大小也为E,一电子(-e,m)在y轴上的P(0,d)点以沿x轴正方向的初速度v0开始运动,不计电子重力,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017523594722.png)
⑴电子第一次经过x轴的坐标值;
⑵请在图上画出电子在一个周期内的大致运动轨迹;
⑶电子在y方向上运动的周期;
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017523594722.png)
⑴电子第一次经过x轴的坐标值;
⑵请在图上画出电子在一个周期内的大致运动轨迹;
⑶电子在y方向上运动的周期;
(1) (
,0) (2)见下图 (3) ![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752390841.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017524219723.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752375879.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752390841.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017524219723.png)
试题分析:⑴在y>0空间中,沿x轴正方向以v0的速度做匀速直线运动,沿y轴负方向做匀加速直线运动,设其加速度大小为a,则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752437638.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752453711.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752468513.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752484884.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752499980.png)
因此电子第一次经过x轴的坐标值为:(
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752375879.png)
⑵电子轨迹如题答图所示.(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017525319858.png)
在y<0空间中,沿x轴正方向仍以v0的速度做匀速直线运动,沿y轴负方向做匀减速直线运动,设其加速度大小也为a,由对称性可知:电子在y轴方向速度减小为零时的时间:t2 = t1 =
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752546781.png)
电子沿x轴方向移动的距离为:x2 = x1 =
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001752375879.png)
(3)电子在y轴方向的运动周期:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017525771245.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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