题目内容
如图所示,质量为M的平板小车静止在光滑的水乎地面上,小车左端放一个质量为m的木块,车的右端固定一个轻质弹簧,现给木块一个水平向右的瞬时冲量I,木块便沿小车向右滑行,在与弹簧相碰后又沿原路返回,并且恰好能到达小车的左端。试求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500510198715498.png)
①木块返回到小车左端时小车的动能;
②弹簧获得的最大弹性势能。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500510198715498.png)
①木块返回到小车左端时小车的动能;
②弹簧获得的最大弹性势能。
①
;②![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051020491501.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051020331207.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051020491501.png)
试题分析:①选小车和木块整体为研究对象,由于m受到冲量I之后系统水平方向不受外力作用,系统动量守恒,设系统的末速度为v,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825005102096688.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051021111043.png)
小车的动能为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825005102127673.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051020331207.png)
②当弹簧具有最大弹性势能
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825005102221395.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825005102236460.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051022522007.png)
当木板返回到小车左端时,由能量守恒得
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051023141868.png)
联立得
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250051020491501.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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