题目内容
如图所示,轻绳的两端分别系在圆环A和小球B上,圆环A套在粗糙的水平直杆MN上。现用水平力拉着绳子上的一点O,使小球B从图中实线位置缓慢上升到虚线位置,但圆环A始终保持在原位置不动。则在这一过程中,环对杆的摩擦力f和环对杆的压力FN的变化情况是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022067642515.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022067642515.png)
A.f不变,FN不变 | B.f增大,FN不变 |
C.f增大,FN减小 | D.f不变,FN减小 |
B
试题分析:以结点O为研究对象,进行受力分析,如图1所示,其中
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206780589.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206795700.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206811297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206827302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206842418.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206858849.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206873304.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002206889411.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022069055446.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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