题目内容
如图甲所示,水平放置足够长的平行金属导轨,左右两端分别接有一个阻值为R的电阻,匀强磁场与导轨平面垂直,质量m =" 0.1" kg、电阻r =
的金属棒置于导轨上,与导轨垂直且接触良好。现用一拉力F =(0.3+0.2t)N作用在金属棒上,经过2s后撤去F,再经过0.55s金属棒停止运动。图乙所示为金属棒的v–t图象,g = 10m/s2。求:
小题1:金属棒与导轨之间的动摩擦因数;
小题2:整个过程中金属棒运动的距离;
小题3:从
撤去F到金属棒停止的过程中,每个电阻R上产生的焦耳热。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306362556656.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636099409.png)
小题1:金属棒与导轨之间的动摩擦因数;
小题2:整个过程中金属棒运动的距离;
小题3:从
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636193161.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306362556656.png)
小题1:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636427815.png)
小题2:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636458661.png)
小题3:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306364891109.png)
(1)在0-2s这段时间内,根据牛顿第二定律 有![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636520169.png)
(2分)
由图可知
(1分)
又因
联立解得
,
(1分)
(1分)
(2) 在0--2s这段时间内的位移为
(1分)
设棒在2---2.55s时间内的位移为
,
棒在 t时刻,根据牛顿第二定律 有
(1分)
在t到t+
(
)时间内
(1分)
(1分)
(1分)
代入数据得
m
整个过程中金属棒运动的距离
m (1分)
(3)从撤去拉力到棒停止的过程中,根据能量守恒定律 有
(2分)
J (1分)
每个电阻R上产生的焦耳热
J (2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636520169.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306365671203.png)
由图可知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636614658.png)
又因
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636645570.png)
联立解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636692474.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636520169.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636427815.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636817164.png)
(2) 在0--2s这段时间内的位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306368481024.png)
设棒在2---2.55s时间内的位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636895334.png)
棒在 t时刻,根据牛顿第二定律 有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306369261252.png)
在t到t+
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636957374.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636988479.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306370201285.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306370821528.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306371291171.png)
代入数据得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130637160554.png)
整个过程中金属棒运动的距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130636458661.png)
(3)从撤去拉力到棒停止的过程中,根据能量守恒定律 有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306373321117.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130637347601.png)
每个电阻R上产生的焦耳热
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306364891109.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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