题目内容
用三根轻绳将质量为m的物块悬挂在空中,如图所示.已知ac和bc与竖直方向的夹角分别为
和
,则ac绳的拉力分别为 bc绳中的拉力为 。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241651067072200.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165105896398.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165106302411.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241651067072200.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165106910768.png)
试题分析:对结点C受力分析,受点c到三根绳子拉力,将Fa和Fb合成为F,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241651085173343.jpg)
根据三力平衡得出:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165108610602.png)
已知ac和bc与竖直方向的夹角分别为30°和60°,所以α=30°
根据三角函数关系得出:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241651089221693.png)
点评:该题的关键在于能够对结点c进行受力分析,利用平衡状态条件解决问题.力的计算离不开几何关系和三角函数.
![](http://thumb2018.1010pic.com/images/loading.gif)
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