题目内容
如图所示,长为L的轻杆的下端用铰链固接在水平地面上,上端固定一个质量为m的小球,轻杆处于竖直位置,同时与一个质量为M的长方体刚好接触。由于微小扰动,杆向右侧倒下,当小球与长方体分离时,杆与水平面的夹角为30°,且杆对小球的作用力恰好为零,若不计一切摩擦。则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022270444837.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022270444837.jpg)
A.长方体与小球的质量比是4 :1 |
B.分离时小球的速率为![]() |
C.分离后长方体的速率为![]() |
D.长方体对小球做功-mgL/4 |
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试题分析:在杆从竖直位置开始倒下到小球与长方体恰好分离的过程中,小球和长方体组成的系统机械能守恒,小球和长方体的速度分别为v1和v2,则有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022270911418.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227107958.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227122672.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227138656.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227107958.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227169676.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227185766.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250022272001367.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002227216845.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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