题目内容
物体在合外力作用下做直线运动的v一t图象如图所示。下列表述正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241925094742759.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241925094742759.jpg)
A.在0—1s内,合外力做正功 |
B.在0—2s内,合外力总是做负功 |
C.在1—2s内,合外力不做功 |
D.在0—3s内,合外力总是做正功 |
A
试题分析:在0~ls内,动能增加,根据动能定理
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824192509973733.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824192509973733.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824192509973733.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824192509973733.png)
故选A.
点评:解决本题的关键会熟练运用动能定理
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824192509973733.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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