题目内容
一轻绳跨过两个等高的定滑轮(不计大小和摩擦),两
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241151250082773.jpg)
端分别挂上质量为m1=4kg和m2=2kg的物体,如图所示。在滑
轮之间的一段绳上悬挂物体m,为使三个物体能保持平衡,求
m的取值范围。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241151250082773.jpg)
端分别挂上质量为m1=4kg和m2=2kg的物体,如图所示。在滑
轮之间的一段绳上悬挂物体m,为使三个物体能保持平衡,求
m的取值范围。
2
Kg<m<6Kg
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125024225.gif)
平衡时,O点受力如图所示
建立方程![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125070709.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125117595.gif)
将
代入得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125164531.gif)
所以
进行如下讨论:
当θ2=0时,m最大mmax=6Kg,当=90°,m最小mmin=2
Kg.
因为θ2=0、θ2=90°时取不到,故m平衡时的取值范围是2
Kg<m<6Kg.
建立方程
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125070709.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125117595.gif)
将
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125117778.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125133612.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125164531.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125304878.gif)
当θ2=0时,m最大mmax=6Kg,当=90°,m最小mmin=2
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125024225.gif)
因为θ2=0、θ2=90°时取不到,故m平衡时的取值范围是2
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115125024225.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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