题目内容
如图所示,三个相同的木块放在同一个水平面上,木块和水平面间的动摩擦因数相同。分别给它们施加一个大小均为F的作用力,其中给第一、三两木块的推力或拉力与水平方向的夹角相同,这时三个木块都保持静止。比较它们和水平面间的弹力大小FN1、FN2、FN3和摩擦力大小Ff1、Ff 2、Ff 3,下列说法中正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241540245451241.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154024607193.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241540245451241.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154024607193.png)
A.FN 1>FN 2>FN 3,Ff 1>Ff 2>Ff 3 | B.FN 1=FN 2=FN 3,Ff 1=Ff 2=Ff 3 |
C.FN 1>FN 2>FN 3,Ff 1=Ff 3<Ff 2 | D.FN 1>FN 2>FN 3,Ff 1=Ff 2=Ff 3 |
C
试题分析:三个木块都保持静止,对三个木块进行受力分析:
对于1木块,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154024717868.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154025138648.png)
对于2木块,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154025543637.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154025621478.png)
对于1木块,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154025715858.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154025777668.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154025887951.png)
故选C
点评:处于静止状态的物体,求静摩擦力大小一般用共点力平衡,在有摩擦力的方向上合力为零。
![](http://thumb2018.1010pic.com/images/loading.gif)
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