题目内容
如图,竖直环A半径为r,固定在木板B上,木板B放在水平 地面上,B的左右两侧各有一档板固定在地上,B不能左右运动,在环的最低点静放有一小球C,A.B.C的质量均为m。给小球一水平向右的瞬时速度V,小球会在环内侧做圆周运动,为保证小球能通过环的最高点,且不会使环在竖直方向上跳起,(不计小球与环的摩擦阻力),瞬时速度必须满足
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250003396623123.jpg)
A.最小值
B.最大值
C.最小值
D.最大值![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339958477.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250003396623123.jpg)
A.最小值
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339693491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339818503.png)
C.最小值
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339942474.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339958477.png)
CD
试题分析:据题意,先假设小球到达最高点时,小球和环之间没有相互作用力,则小球做圆周运动的向心力有小球的重力提供,则有:mg=mv2/r,则v=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339974430.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339942474.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000340020515.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000339958477.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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