题目内容
如图有一个足够长倾角α=30º的斜坡,一个小孩在做游戏时,从该斜坡顶端将一足球沿水平方向水平踢出去,已知足球被踢出时的初动能为9J,则该足球第一次落在斜坡上时的动能为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241334126041175.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241334126041175.png)
A.12J | B.21J | C.27J | D.36J |
B
由Ek0=mv02/2得
,h=gt2/2, x=v0t
,联立以上各式得
,由
得
,
12+9=21J,B对。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241334129001512.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133412650689.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133412697731.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241334127281000.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133412760740.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133412806795.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241334128691262.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241334129001512.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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A.12J | B.21J | C.27J | D.36J |