题目内容
如图所示,在光滑水平面上的物体,受四个沿水平面的恒力
、
、
和
作用,以速率
沿水平面做匀速运动,若撤去其中某个力(其他力不变)一段时间后又恢复该作用力,结果物体又能以原来的速率
匀速运动,这个力是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241540553553180.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154054700293.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154054856295.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055027303.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055121321.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055183341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055183341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241540553553180.jpg)
A.![]() | B.![]() | C.![]() | D.![]() |
B
试题分析:A、撤去
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055823333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055901323.png)
B、撤去
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055963353.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055963353.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055901323.png)
C、撤去
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154056229366.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055901323.png)
D、撤去
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154056447355.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154055901323.png)
故选B
点评:本题物体只能先减速后加速度才行,只有合力与初速度成钝角时,物体才能先减速后加速。
![](http://thumb2018.1010pic.com/images/loading.gif)
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A.![]() | B.![]() | C.![]() | D.![]() |