题目内容
如图所示,足够长的U形导体框架的宽度l =" 0.5" m,电阻忽略不计,其所在平面与水平面成
角,磁感应强度B =" 0.8" T的匀强磁场方向垂直于导体框平面,一根质量m =" 0.2" kg,有效电阻R = 2Ω的导体棒MN垂直跨放在U形框架上,导体棒与框架间的动摩擦因数
=0.5,导体棒由静止开始沿框架下滑到刚开始匀速运动,通过导体棒截面的电量共为Q =" 2" C。求:
(1)导体棒匀速运动的速度;
(2)导体棒从开始下滑到刚开始匀速运动这一过程中,导体棒的电阻产生的焦耳热。
(sin 37°= 0.6,cos 37°= 0.8,g = 10m/s2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333194083717.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319314431.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319361301.png)
(1)导体棒匀速运动的速度;
(2)导体棒从开始下滑到刚开始匀速运动这一过程中,导体棒的电阻产生的焦耳热。
(sin 37°= 0.6,cos 37°= 0.8,g = 10m/s2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333194083717.png)
(1)设导体棒匀速的速度为v
2分
,
,
2分
由以上各式得:v=
="5" m/s 1分
(2)通过导体的电量
设物体下滑的距离为s,则
由以上各式得:
,s=
="10" m 2分
全程由动能定理得:
2分
得:
1分
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333194391052.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319486596.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319548521.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319579555.png)
由以上各式得:v=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333196261200.png)
(2)通过导体的电量
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319704558.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319766841.png)
设物体下滑的距离为s,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319829632.png)
由以上各式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319891884.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319954573.png)
全程由动能定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333199851539.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133320063631.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133320094483.png)
(1)设导体棒匀速的速度为v
2分
,
,
2分
由以上各式得:v=
="5" m/s 1分
(2)通过导体的电量
设物体下滑的距离为s,则
由以上各式得:
,s=
="10" m 2分
全程由动能定理得:
2分
得:
1分
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333194391052.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319486596.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319548521.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319579555.png)
由以上各式得:v=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333196261200.png)
(2)通过导体的电量
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319704558.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319766841.png)
设物体下滑的距离为s,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319829632.png)
由以上各式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319891884.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133319954573.png)
全程由动能定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241333199851539.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133320063631.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133320094483.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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