题目内容
圆形光滑轨道位于竖直平面内,其半径为R,质量为m的金属小环套在轨道上,并能自由滑动,如图所示,以下说法正确的是 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241332476777358.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241332476777358.png)
A.要使小环能通过轨道的最高点,小环通过最低点时的速度必须大于![]() |
B.要使小环能通过轨道的最高点,小环通过最低时的速度必须大于![]() |
C.如果小圆环在轨道最高点时的速度等于![]() |
D.如果小圆环在轨道最高点时的速度小于![]() |
BCD
小环到达最高点的最小速度大于零,根据机械能守恒,有
,则
,A错误、B正确;当最高点时的速度等于
,有
,
,根据牛顿第三定律,小环挤压轨道内侧,C正确;当最高点时的速度小于
,有
,
,则小环挤压轨道外侧,D错误。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133247911851.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133248005612.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133247864503.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133248114879.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133248207552.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133247895431.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133248114879.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133248332463.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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