题目内容
如图(a)、(b)所示,同一物体分别在外力F1、F2作用下均能静止在斜面上,F1、F2大小相等,方向与斜面夹角均为α,图(a)中物体与斜面间的弹力大小为N1、摩擦力大小为f1,图(b)中物体与斜面间的弹力大小为N2、摩擦力大小为f2,则下列判断正确的( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241506039376294.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241506039376294.jpg)
A.N1< N2,f1<f2 | B.N1= N2,f1<f2 |
C.N1< N2,f1=f2 | D.N1= N2,f1=f2 |
C
试题分析:(a)(b)图中物体受到重力,斜面的支持力,摩擦力,和F四个力作用,根据正交分解可得:在沿斜面方向上有:
如果
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150603953939.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604046939.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241506041091013.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604218439.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604312923.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604530395.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604218439.png)
如果
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604748941.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241506048261034.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241506048891012.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150604218439.png)
综上所述,两者的摩擦力相等,AB错误
在沿垂直斜面方向上有:
(a)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150605123950.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150605248990.png)
(b)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150605310966.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150605419529.png)
点评:做此类型题目的关键是正确对物体受力分析,然后运用正交分解法列等式求解
![](http://thumb2018.1010pic.com/images/loading.gif)
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