题目内容
如图所示,滑块质量为m,与水平地面的动摩擦因数为0.1,它获得一大小为3
的水平速度后,由A向B滑行5R,并滑上光滑的半径为R的
圆弧BC,在C点的正上方有一离C高度也为R的旋转平台,沿平台直径方向开有两个离轴心距离相等的小孔P、Q,旋转时两孔均能达到C点的正上方,若滑块过C点后穿过P,又恰能从Q孔落下,则平台的角速度ω应满足什么条件?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553488822124.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155348711429.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155348789303.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553488822124.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553490851651.png)
试题分析:滑块以速度,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155349288272.png)
滑块由A滑到B过程中,由动能定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155349397430.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155349475272.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155349662425.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155349756286.png)
滑块穿过P孔后竖直上抛,上抛到落回的总共时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155349912360.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553500682804.png)
平台转过角度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155350271279.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553504891624.png)
式中(n=0、1、2……)
点评:本题的易错点在于平台转动的角速度的多解性,注意运动的周期性往往带来多解性.
![](http://thumb2018.1010pic.com/images/loading.gif)
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