题目内容
如图所示,两根相距为
=1m的足够长的平行光滑金属导轨,位于水平的xOy平面内,一端接有阻值为
的电阻.在
的一侧存在垂直纸面向里的磁场,磁感应强度B只随x的增大而增大,且它们间的关系为B=
x,其中![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120422332.jpg)
。一质量为m=0.5kg的金属杆与金属导轨垂直,可在导轨上滑动.当t=0时金属杆位于x=0处,速度为
=
,方向沿x轴的正方向。在运动过程中
,有一大小可调节的外力F作用于金属杆,使金属杆以恒定加速度a=
沿x轴正方向匀加速直线运动。除电阻R以外其余电阻都可以忽略不计.求:当t=4s时施加于金属杆上的外力为多大。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211205326386.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120360185.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120376301.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120391243.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120407199.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120422332.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120438456.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120469205.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120485360.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120422332.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120516386.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211205326386.jpg)
5N
解:根据匀变速直线运动的速度公式可得t=4s时的速度为
(2分)
根据匀变速直线运动的位移公式可得t=4s时的位移为
(2分)
由B=
x可得t=4s时磁感应强度B=2T (2分)
t=4s时的感应电动势
(2分)
t=4s时的回路感应电流
(2分)
t=4s时金属杆所受的安培力为
(2分)
由牛顿第二定律
(2分)
得
(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120547800.gif)
根据匀变速直线运动的位移公式可得t=4s时的位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211205631011.gif)
由B=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120563251.gif)
t=4s时的感应电动势
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120578644.gif)
t=4s时的回路感应电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120594625.gif)
t=4s时金属杆所受的安培力为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120610693.gif)
由牛顿第二定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120625462.gif)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121120641789.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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