题目内容
如图所示,一个小球在竖直环内至少能做(n+1)次完整的圆周运动,当它第(n-1)次经过环的最低点时的速度大小为7m/s,第n次经过环的最低点时速度大小为5m/s,则小球第(n+1)次经过环的最低点时的速度v的大小一定满足
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000323991277.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000323991277.jpg)
A.等于3m/s | B.小于1m/s |
C.等于1m/s | D.大于1m/s |
D
试题分析:设物体质量为m,根据动能定理,第n次做圆周运动时克服摩擦力做的功
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000324771519.png)
若第n+1次克服摩擦力做有相同,
则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000325081528.png)
可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000032508642.png)
而实际运动过程中经同一点时,速度越来越小,需要的向心力越来越小,对轨道的压力也会越来越小,而滑动摩擦力
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000032524570.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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