题目内容
在水平面上,一物体在水平力F作用下运动,其水平力随时间t变化的图像及物体运动的V-t图像如图。由两个图像可知,10s内( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082416445352310063.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082416445352310063.png)
A.水平力F做的功为60J |
B.克服摩擦力做的功为40J |
C.摩擦力做的功为40J |
D.合力功为0 |
BD
试题分析:物体在6-8s内做匀速运动,所以拉力F等于摩擦力,故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164453867607.png)
在0-2s内物体处于静止,所以F做功为零,
在2-6s内物体做匀加速直线运动,发生的位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164454241852.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164454413775.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164454584795.png)
在6-8s内物体匀速直线运动,发生的位移为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164454756743.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164454943806.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164455130621.png)
在8-10s内拉力为零,做功为零
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164455302523.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164455473971.png)
所以F做功为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164455645574.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164455910650.png)
点评:本题的关键是从题中的v-t图像中得出物体的运动情况,然后根据恒力做功计算
![](http://thumb2018.1010pic.com/images/loading.gif)
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