题目内容
如图所示,长为L的轻杆,一端固定一个小球,另一端固定在光滑的水平轴上,使小球在竖直平面内做圆周运动,关于小球在最高点的速度和受力情况,下列说法正确的是:( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164420826411.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241644204982287.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164420826411.png)
A.小球的速度的最小值为 |
B.小球在最高点的速度v由0逐渐增大时,轻杆对球的作用力逐渐减小 |
C.小球在最高点的速度v由0逐渐增大时,轻杆对球的作用力逐渐增大 |
D.小球在最高点的速度v由0逐渐增大时,轻杆对球的作用力先减小再增大 |
D
试题分析:杆的作用力能产生向上的弹力,当向上的弹力F=mg时,小球速度为零,A错;向心力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164420997712.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164421200512.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164421418528.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164421606830.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164421762542.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164421964846.png)
点评:解决本题的关键知道小球在最高点的临界情况,知道向心力的来源,运用牛顿第二定律进行求解.
![](http://thumb2018.1010pic.com/images/loading.gif)
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