题目内容
如右图所示,质量为m的小球用细线拴住放在光滑斜面上,斜面足够长,倾角为
的斜面体置于光滑水平面上,用水平力F推斜面体使斜面体缓慢地向左移动,小球沿斜面缓慢升高。当线拉力最小时,推力F等于( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241608458532777.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160845603310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241608458532777.jpg)
A.![]() | B.![]() | C.![]() | D.![]() |
D
试题分析:对小球受力分析如图所示,重力的大小方向不变,平移另两个力构成一首尾相连的闭合的三角形,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241608472268365.jpg)
滑块左移会引起
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160847257364.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160847382411.png)
如图所示:则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160847257364.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160847382411.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160847257364.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160848240440.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160848427743.png)
对斜面研究,可得在水平方向上,有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160848567659.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241608487861495.png)
故选D,
点评:做本题的关键是知道什么时候绳子的拉力最小,然后根据力的矢量三角形判断
![](http://thumb2018.1010pic.com/images/loading.gif)
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