题目内容
如图所示,光滑的倾斜轨道与半径为R的圆形轨道相连接,质量为m的小球在倾斜轨道上由静止释放,要使小球恰能通过圆形轨道的最高点,小球释放点离圆形轨道最低点的高度为( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241952084452936.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241952084452936.png)
A.2.5R | B.2R |
C.5R | D.3R |
A
试题分析:小球恰好能通过最高点,则满足在最高点重力完全充当向心力,根据牛顿第二定理有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195209209762.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195209521578.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241952101141040.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195211003556.png)
故选A
点评:常规题,本题的突破口是抓住在C点时小球恰好能通过的临界条件,
![](http://thumb2018.1010pic.com/images/loading.gif)
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