题目内容
如图所示,轻弹簧k一端与墙相连,处于自然状态,质量为4 kg的木块沿光滑的水平面以5m/s的速度运动并开始挤压弹簧.求弹簧的最大弹性势能及木块被弹回速度增大到3m/s时弹簧的弹性势能.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241934193902456.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241934193902456.jpg)
32 J
试题分析:物体和弹簧构成的系统机械能守恒,当弹簧的弹性势能最大时,物体的动能为零,由机械能守恒定律得,弹簧的最大弹性势能为
Epm=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
当物体的速度为v="3" m/s时,弹簧的弹性势能为Ep,由机械能守恒定律得
Ep+
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
Ep=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824193419671338.png)
点评:以弹簧和木块组成的系统为研究对象,只有弹力做功,系统的机械能守恒.初态时,系统只有木块的动能,当木块被弹回速度增大到3m/s时,木块有动能、弹簧有弹性势能,根据机械能守恒定律求解木块被弹回速度增大到3m/s时弹簧的弹性势能.
![](http://thumb2018.1010pic.com/images/loading.gif)
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