题目内容
(10分)如图所示,固定于水平桌面上足够长的两平行光滑导轨PQ、MN,其电阻不计,间距d=0.5m,P、M两端接有一只理想电压表,整个装置处于竖直向下的磁感应强度B0=0.2T的匀强磁场中,两金属棒L1、L2平行地搁在导轨上,其电阻均为r=0.1Ω,质量分别为M1=0.3kg和M2=0.5kg。固定棒L1,使L2在水平恒力F=0.8N的作用下,由静止开始运动。试求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250012337282855.png)
(1) 当电压表读数为U=0.2V时,棒L2的加速度为多大;
(2)棒L2能达到的最大速度vm.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250012337282855.png)
(1) 当电压表读数为U=0.2V时,棒L2的加速度为多大;
(2)棒L2能达到的最大速度vm.
(1)1.2m/s2 (2)16m/s
试题分析:(1) 流过L2的电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233744902.png)
L2所受的安培力
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233760834.png)
对L2由牛顿第二定律,可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233775640.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233791616.png)
(2)当安培力
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233822401.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233838302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233853682.png)
而
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233869769.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001233884463.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250012339161092.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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