题目内容
(12分)如图13所示:宽度L=1m的足够长的U形金属框架水平放置,框架处在竖直向上的匀强磁场中,磁感应强度B=1T,框架导轨上放一根质量m=0.2kg、电阻R=1.0Ω的金属棒ab,棒ab与导轨间的动摩擦因数μ=0.5,现用功率恒为6w的牵引力F使棒从静止开始沿导轨运动(ab棒始终与导轨接触良好且垂直),当棒的电阻R产生热量Q=5.8J时获得稳定速度,此过程中,通过棒的电量q=2.8C(框架电阻不计,g取10m/s2)。问:
(1)ab棒达到的稳定速度多大?
(2)ab棒从静止开始到稳定速度所经历时间是多少?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241212489212308.jpg)
(1)ab棒达到的稳定速度多大?
(2)ab棒从静止开始到稳定速度所经历时间是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241212489212308.jpg)
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121248968399.gif)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121248984262.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121248968399.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121248984262.gif)
(1)
… ① (1分)
… ② (1分)
… ③ (1分)
棒稳定时:
… ④ (1分)
由①②③④联立解得
(2分)
(2)由能量守恒得:
① (2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249327928.gif)
② (2分)
(直接写出
得出②式亦可得分)
由①②联立解得:
(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249031272.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249109431.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249124344.gif)
棒稳定时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249140498.gif)
由①②③④联立解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121248968399.gif)
(2)由能量守恒得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249249750.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249327928.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249421598.gif)
(直接写出
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121249436389.gif)
由①②联立解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121248984262.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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