题目内容
如图所示,用与竖直方向成θ角的倾斜轻绳子a和水平轻绳子b共同固定一个小球,这时绳b的拉力为F1.现在保持小球在原位置不动,使绳子b在原竖直平面内,逆时针转过θ角固定,绳b拉力变为F2;再转过θ角固定,绳b拉力变为F3,则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043031752920.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043031752920.png)
A.F1<F2<F3 | B.F1= F3>F2 |
C.F1= F3<F2 | D.绳a拉力一直减小 |
BD
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043031904564.png)
试题分析:据题意,b绳第一次转过θ角后F2与a绳拉力Fa垂直,再转过θ角后,F3和F1关于F2对称,则有
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004303237440.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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