题目内容
如图所示,位于水平桌面上的物块P,由跨过定滑轮的轻绳与物块Q相连,从滑轮到P和到Q的两段绳都是水平的。已知Q与P之间以及P与桌面之间的动摩擦因数都是μ,Q质量为m,P质量为2m,滑轮的质量、滑轮轴上的摩擦都不计,若用一水平向右的力F拉Q使它做匀速运动,则F的大小为( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400141204339.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400141204339.jpg)
A.6μmg | B.5μmg | C.3μmg | D.μmg |
B
设PQ之间的摩擦力为
即
,P与地面之间的摩擦力为
即
,绳子间的张力为T,对Q受力分析得
,对P受力分析得
,所以
,选B
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014135326.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014198604.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014244348.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014307677.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014385525.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014432542.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140014478675.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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