题目内容
载人气球原静止于高h的空中,气球质量为M,人的质量为m。若人要沿绳梯着地,则绳梯长至少是( )
A.(m+M)h/M | B.mh/M | C.Mh/m | D.h |
A
设人下滑的速度为v其方向为正方向,气球上升的速度为
,对人、气球和绳梯构成的系统动量守恒,mv-M
=0,h=vt,
,三式联立解得
=(m+M)h/M ,A对,BCD错。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134849403308.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134849403308.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134849918556.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134849980280.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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题目内容
A.(m+M)h/M | B.mh/M | C.Mh/m | D.h |