题目内容
一根质量为m、长为L的均匀链条一半放在光滑的水平桌面上,另一半挂在桌边,桌面足够高,如图(a)所示。若在链条两端各挂一个质量为
的小球,如图(b)所示。若在链条两端和中央各挂一个质量为
的小球,如图(c)所示。由静止释放,当链条刚离开桌面时,图(a)中链条的速度为va,图(b)中链条的速度为vb,图(c)中链条的速度为vc(设链条滑动过程中始终不离开桌面,挡板光滑)。下列判断中正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413041955210584.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419490461.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419490461.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413041955210584.png)
A.va=vb=vc | B.va<vb<vc |
C.va>vb>vc | D.va>vc>vb |
D
根据机械能守恒定律a、
,解得![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419646686.png)
b、
,解得![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419708665.png)
c、
,解得![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419770712.png)
所以可知
,选D
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419583916.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419646686.png)
b、
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304196771139.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419708665.png)
c、
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304197391116.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419770712.png)
所以可知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130419817539.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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