题目内容
如图所示,质量为
的小木块A 一水平初速度
冲上质量M、长为
、置于光滑水平面的木块B ,并正好不从B木块上掉下,A、B间动摩擦因数为
,求此过程A、B物体组成的系统减少的动能。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242013212981454.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201317975338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201318614326.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201319223281.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201320252322.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242013212981454.png)
A、B动能的变化量为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201322265596.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201322265596.png)
试题分析:A正好不从B木块上掉下,说明A运动到B的最右端时AB速度相等,设该速度为v。
如图,对A、B物体分别列动能定理式
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242013229513921.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242013232941149.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242013243861011.png)
由(1)、(2)可得,
即此过程A、B物体组成的系统减少的动能
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201325510582.png)
点评:本题通过对系统内力的摩擦力分析做功,在分析动能定理时,要弄清是那些力对物体做功,并分清功能转换关系。
![](http://thumb2018.1010pic.com/images/loading.gif)
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