题目内容
如图2所示,在高1.5 m的光滑平台上有一个质量为2 kg的小球被一细线拴在墙上,球与墙之间有一根被压缩的轻质弹簧.当烧断细线时,小球被弹出,小球落地时的速度方向与水平方向成60°角,则弹簧被压缩时具有的弹性势能为(g=10 m/s2) ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241418324553375.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241418324553375.jpg)
A.10 J | B.15 J | C.20 J | D.25 J |
A
由h=
gt2和vy=gt得:vy=
m/s,
落地时,tan60°=
可得:
v0=
=
m/s,
由机械能守恒得:Ep=
mv02,
可求得:Ep=10 J,故A正确.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141832767338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141832814410.png)
落地时,tan60°=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141833157451.png)
v0=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141833219691.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141833251363.png)
由机械能守恒得:Ep=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141832767338.png)
可求得:Ep=10 J,故A正确.
![](http://thumb2018.1010pic.com/images/loading.gif)
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