题目内容
如图所示,竖直杆OB顶端有光滑轻质滑轮,轻质杆OA自重不计,可绕O点自由转动,OA=OB.当绳缓慢放下,使∠AOB由0°逐渐增大到180°的过程中(不包括0°和180°),下列说法正确的是(A是结点)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242336361205293.png)
A.AB绳上的拉力先逐渐增大后逐渐减小
B.OA杆上的压力先逐渐减小后逐渐增大
C.AB绳上的拉力越来越大,但不超过2G
D.OA杆上的压力大小始终等于G
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242336361205293.png)
A.AB绳上的拉力先逐渐增大后逐渐减小
B.OA杆上的压力先逐渐减小后逐渐增大
C.AB绳上的拉力越来越大,但不超过2G
D.OA杆上的压力大小始终等于G
CD
试题分析:端点的受力图如图所示,由力的三角形法则可知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824233636884926.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824233637711503.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824233639131450.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242336405665576.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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