题目内容
如图7-7-10所示,质量为2m和m的可看作质点的小球A、B,用不计质量、不可伸长的细线相连,跨在固定的光滑圆柱两侧.开始时,A球和B球与圆柱轴心同高,然后释放A球,则B球到达最高点时的速率是多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204423881883.jpg)
图7-7-10
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204423881883.jpg)
图7-7-10
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120442403618.gif)
选轴心所在水平面为参考平面,则刚开始时系统的机械能E1=0.当B球到达最高点时,细线被A球拉下的长度为
×2πR,此时A、B两球的重力势能分别为EpB=mgR,EpA=-2mg×
.所以此时系统的机械能为
根据机械能守恒定律有E1=E2所以
,解得
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120442419221.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120442435399.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204424501101.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204424661076.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120442622669.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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