题目内容
如图所示,作用于O点的三个力平衡。其中一个力为F1,沿-y方向,另一个大小未知的力F2与+x方向夹角θ,下列说法正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241319441811821.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241319441811821.png)
A.力F3的最小值为![]() |
B.力F3只可能在第二象限 |
C.力F3可能在第三象限的任意区 |
D.力F3与F2夹角越小,则力F3与F2越小 |
A
根据力的平衡可知
存在于第三,第四象限中,且当
与
垂直时,
最小,根据正交分解可得力F3的最小值为
,因为三个力平衡,所以无论
与
的夹角如何,他们的合力都等于
,所以A正确。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944290366.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944290366.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944353353.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944290366.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944244514.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944290366.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944353353.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131944556333.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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