题目内容
如图甲所示,固定在水平桌面上的光滑金属导轨cd、eg处于方向垂直导轨向下的匀强磁场中,金属杆ab与导轨接触良好。在两根导轨的端点C、e之间连接一电阻,其他部分电阻忽略不计。现用一水平向右的外力F1作用在金属杆ab上,使金属杆ab向右沿导轨滑动,滑动过程中金属杆ab始终垂直于导轨。金属杆ab受到的安培力用F2表示,F1与F2随时间t变化的关系图像如图乙所示,下面关于金属杆ab运动过程中的v -t图像正确的是![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241324442486683.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241324442794618.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241324442486683.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241324442794618.png)
D
以金属杆
为研究对象,根据牛顿第二定律有
,而
,由题中图乙可知
均匀增大,则
,故
,由此可知金属杆ab所受合外力恒定,做做初速度为零的匀加速运动,故选项D正确
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132444404380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132444451664.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241324446071012.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132444653355.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132444685858.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132444716993.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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