题目内容
如图所示,质量均为m的小球A、B用两根不可伸长的轻绳连接后悬挂于D点,在外力F的作用下,小球A、B处于静止状态,若要使两小球处于静止状态且悬线OA与竖直方向的夹角
保持30°不变,则外力F的大小不可能是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241320533832466.png)
A.可能为mg
B.可能为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053414653.png)
C.可能为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053508546.png)
D.可能为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053555645.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053336302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241320533832466.png)
A.可能为mg
B.可能为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053414653.png)
C.可能为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053508546.png)
D.可能为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053555645.png)
D
根据三角形定则可得当F与绳子拉力T方向垂直时,F最小,有
,所以F不能小于
,故D不可能。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241320536011003.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132053633555.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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