题目内容
如下图所示,在水平粗糙横杆上,有一质量为m的小圆环A,用一细线悬吊一个质量为m的球B。现用一水平拉力缓慢地拉起球B,使细线与竖直方向成37°角,此时环A仍保持静止(sin37°=0.6,cos37°=0.8),求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023477123832.jpg)
(1)此时水平拉力F的大小;
(2)环对横杆的压力及环受到的摩擦力。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023477123832.jpg)
(1)此时水平拉力F的大小;
(2)环对横杆的压力及环受到的摩擦力。
(1)
(2)对横杆的压力大小为2mg,方向竖直向下,环受到的摩擦力大小为
,方向水平向左
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002347852676.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002347868584.png)
试题分析:(1)以B为研究对象知B受重力、拉力F及绳子拉力,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002347899851.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002347852676.png)
(2)把A、B视为一整体知,受力如图所示:整体处于平衡状态,所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002347930667.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002347946780.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023479771184.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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