题目内容
三段不可伸长的细绳OB、OC能承受的最大拉力相同,OA能承受的最大拉力是OB、OC的
倍,它们共同悬挂一重物,如图所示,其中OA与竖直方向夹角是30。,OB是水平的,A端、B端固定。若逐渐增加C端所挂物体的质量,则最先断的绳( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155826360394.png)
A.必定是OA B.必定是OB
C.必定是OC D.可能是OA
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155826157337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155826360394.png)
A.必定是OA B.必定是OB
C.必定是OC D.可能是OA
C
试题分析:O点受到三个拉力,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155826516607.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241558267191143.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241558269221144.png)
故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155827078690.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155826157337.png)
点评:本题首先要选择研究对象:结点O;其次关键是作好力图,就能直观比较三个绳子拉力的大小.
![](http://thumb2018.1010pic.com/images/loading.gif)
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