题目内容
质量为m的物体在与水平方向成
角的恒力作用下,沿天花板作匀速直线运动,物体与天花板的摩擦系数为
,则物体所受到的摩擦力可以用下面哪些式子表达:( )![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436563899.png)
A
B
C
D ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436829830.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436517302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436532306.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436563899.png)
A
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436673507.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436704504.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436797831.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125436829830.png)
BC
物体受重力、支持力、推力及摩擦力而处于平衡状态;将拉力F分解到水平和竖直两个方向,则在水平方向有:Fcosθ=f;故A错误B正确
竖直方向有:G=Fsinθ-FN; 则有:地面对物体的摩擦力f=μFN=μ(Fsin30°-mg),故C正确D错误
所以应该选BC
竖直方向有:G=Fsinθ-FN; 则有:地面对物体的摩擦力f=μFN=μ(Fsin30°-mg),故C正确D错误
所以应该选BC
![](http://thumb2018.1010pic.com/images/loading.gif)
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