题目内容
如图,粗细均匀的U形管的底部中间有一阀门,开始阀门关闭,两臂中的水面高度差为h。现将阀门打开,最终两臂水面相平。则这过程中
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452262893.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452262893.gif)
A.大气压做正功,重力做负功,水的内能不变; |
B.大气压不做功,重力做正功,水的内能增大; |
C.大气压不做功,重力做负功,水的内能增大; |
D.大气压做负功,重力做正功,水的内能不变。 |
B
U形管里的水由高度差h到相平静止这一过程:
大气压做功为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452324928.gif)
重力做功可视为系统重力势能的变化![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452386879.gif)
根据能量守恒定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452464482.gif)
水的内能![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452480519.gif)
∴选B
大气压做功为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452324928.gif)
重力做功可视为系统重力势能的变化
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452386879.gif)
根据能量守恒定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452464482.gif)
水的内能
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114452480519.gif)
∴选B
![](http://thumb2018.1010pic.com/images/loading.gif)
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