题目内容
如图所示,物体在水平推力F的作用下静止在斜面上,若稍微增大水平力F而物体仍保持静止,则下列判断中错误的是 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515477844355.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515477844355.png)
A.斜面对物体的静摩擦力一定增大 |
B.斜面对物体的支持力一定增大 |
C.物体在水平方向所受合力一定增大 |
D.物体在竖直方向所受合力一定不变 |
AC
试题分析:A、对物体进行受力分析,由于推力F大小不确定,所以摩擦力方向也不确定,若
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151547893921.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151547956949.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151548080379.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151548190922.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151548252945.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151548080379.png)
B、对物体进行受力分析有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151548455973.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151548658409.png)
CD、物体处于静止状态合外力为零,所以水平方向所受合力一定为零, 竖直方向所受合力也一定为零;选C不选D
故选AC
点评:本题中摩擦力方向要根据其他外力的合力的方向利用平衡关系分析。
![](http://thumb2018.1010pic.com/images/loading.gif)
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