题目内容
如图甲所示,在粗糙水平面上,物体A在水平向右的外力F的作用下做直线运动,其速度—时间图象如图乙所示,下列判断正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250024310969372.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250024310969372.png)
A.在0~1s内,外力F不断增大 |
B.在1~3s内,外力F的大小恒定 |
C.在3~4s内,外力F不断增大 |
D.在3~4s内,外力F的大小恒定 |
B
试题分析:在0~1s内,直线的斜率不变,加速度不变,外力F是恒力,故A错误.在1~3s内,速度不变,物体做匀速直线运动,加速度等于零,F等于摩擦力,外力F的大小恒定,故B正确.在3~4s内,斜率越来越大,说明加速度越来越大,所以物体做加速度增大的减速运动,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002431111302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002431127304.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002431143592.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002431111302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002431189352.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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