题目内容
如图所示,滑块A1A2由轻杆连结成一个物体,其质量为M,轻杆长L.滑块B的质量为m,长L/2,其左端为一小槽,槽内装有轻质弹簧.开始时,B紧贴A,使弹簧处在压缩状态.今突然松开弹簧,在弹簧作用下整个系统获得动能Ek,弹簧松开后,便离开小槽并远离物体A1A2.以后B将在A1和A2之间发生无机械能损失的碰撞.假定整个系统都位于光滑的水平面上,求物块B的运动周期.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144038242232.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144038242232.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404120791.gif)
设弹簧松开后A1A2物体与物体B的速度各为V和v,则有
①
②
解得
,![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404323791.gif)
B和A碰撞前后
③
④
联立③④式解得
⑤
即碰撞前后,B相对A1A2的速度
的大小不变,只改变方向.
同理可证明,当B与A1碰撞后,也有同样的结果,即相对A1A2,B在以大小不变的相对速度作往返运动.运动的周期为
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404245490.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404260705.gif)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404260820.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404323791.gif)
B和A碰撞前后
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404338644.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404370960.gif)
联立③④式解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404385385.gif)
即碰撞前后,B相对A1A2的速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114404588257.gif)
同理可证明,当B与A1碰撞后,也有同样的结果,即相对A1A2,B在以大小不变的相对速度作往返运动.运动的周期为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144047131054.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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