题目内容
如图所示,A B两物体在同一直线上运动,当它们相距s=7m时,A在水平拉力和摩擦力的作用下,正以4m/s的速度向右做匀速运动,而物体B此时速度为10m/s,方向向右,它在摩擦力作用下做匀减速运动,加速度大小为2m/s2,则A追上B用的时间是 s![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241233448335062.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241233448335062.png)
8
B物体减速到零所需时间,
,若A追上B,B还没停止,则有
,即
,解得t=7s,所以B先停止运动,即
,解得t=8s
故答案为:8
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123344848768.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123344864542.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123344895833.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123344926914.png)
故答案为:8
![](http://thumb2018.1010pic.com/images/loading.gif)
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