题目内容
某同学骑自行车上学时,地面对前轮的摩擦力为F1,对后轮的摩擦力为Ff1 ;推自行车前进时,地面对前轮的摩擦力为F2,对后轮的摩擦力为Ff2则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250021379983061.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250021379983061.jpg)
A.F1与车前进方向相同 |
B.Ff1与车前进方向相同 |
C.F2与车前进方向相同 |
D.Ff2与车前进方向相同 |
B
试题分析:骑车前进时,后轮是主动轮,在它与地面接触处有相对地面向后滑的趋势,故受向前的摩擦力;前轮是从动轮,它在与地面接触处有相对于地面向前滑的趋势,故受向后的摩擦力.即
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002137998369.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002138013333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002138029464.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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