题目内容
如图,在水平桌面上放置两条相距l的平行光滑导轨ab与cd,阻值为R的电阻与导轨的a、c端相连。滑杆MN垂直于导轨并可在导轨上滑动。整个装置放于匀强磁场中,磁场的方向竖直向上,磁感应强度的大小为B。滑杆的中点系一不可伸长的轻绳,绳绕过固定在桌边的光滑轻滑轮后,与一质量为m的物块相连,绳处于拉直状态。现若从静止开始释放物块,用i表示回路中的感应电流,g表示重力加速度,则在物块下落过程中物块的速度可能 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003734764.png)
A.
B.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003812669.png)
C.
D.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003890609.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003734764.png)
A.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003796674.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003812669.png)
C.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003858631.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003890609.png)
AD
物块下落过程中,做加速度逐渐减小的加速运动,若导轨足够长,则最终做匀速运动,即速度最大时,物块的重力等于安培力,即
,所以速度
,故A正确B错误
安培力小于物块重力,所以安培力的功率可能小于重力的功率,即
,所以物块的速度
,故C错误D正确
故选AD
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241230039211369.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003796674.png)
安培力小于物块重力,所以安培力的功率可能小于重力的功率,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003968667.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123003890609.png)
故选AD
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目