题目内容
如图所示,光滑的水平面上有mA=2kg,mB= mC=1kg的三个物体,用轻弹簧将A与B连接.在A、C两边用力使三个物体靠近,A、B间的弹簧被压缩,此过程外力做功72 J,然后从静止开始释放,求当物体B与C分离时,B对C做的功有多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031292393069.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031292393069.jpg)
18J
试题分析:(1)当弹簧恢复原长时,B与C分离,0=mAvA-(mB+mc)vC ①,
EP=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003129254655.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003129270857.png)
对C由动能定理得W=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003129286642.png)
由①②③得W=18J,vA=vC=6m/s.
![](http://thumb2018.1010pic.com/images/loading.gif)
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