题目内容
如图轨道是由一直轨道和一半圆轨道组成,一个小滑块从距轨道最低点B为h的A处由静止开始运动,滑块质量为m,不计一切摩擦。则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241601528265084.jpg)
A.若滑块能通过圆轨道最高点D,h最小为2.5R
B.若h=2R,当滑块到达与圆心等高的C点时,对轨道的压力为3mg
C.若h=2R,滑块会从C、D之间的某个位置离开圆轨道做斜抛运动
D.若要使滑块能返回到A点,则h≤R
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241601528265084.jpg)
A.若滑块能通过圆轨道最高点D,h最小为2.5R
B.若h=2R,当滑块到达与圆心等高的C点时,对轨道的压力为3mg
C.若h=2R,滑块会从C、D之间的某个位置离开圆轨道做斜抛运动
D.若要使滑块能返回到A点,则h≤R
ACD
试题分析:滑块恰好能通过最高点时,重力完全充当向心力,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160152842693.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153029512.png)
滑块下落过程中机械能守恒,所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153138971.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153263527.png)
若h=2R,当滑块到达与圆心等高的C点时,有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153341763.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153435557.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153544839.png)
若h=2R,滑块不能通过最高点,所以会在C、D之间的某个位置离开圆轨道做斜抛运动,C正确,
若要使滑块能返回A点,则滑块不能通过C点,所以则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160153638460.png)
点评:做本题的关键是从最高点的临界状态作为突破口,
![](http://thumb2018.1010pic.com/images/loading.gif)
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