题目内容
如图所示,一长为L轻杆一端固定质量为m的小球,以另一端O为圆心,使得小球在竖直平面内做圆周运动,小球在最高点的速率为v,以下说法正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241228095573373.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241228095573373.png)
A.v的最小值是0 |
B.小球过最高点时,杆对小球的弹力一定为零 |
C.v由![]() |
D.v由![]() |
AD
A、杆既可以提供拉力,又可以提供支持力,所以小球到达最高点时的速度可以等于零,故A正确;
B、小球在最高点时,如果速度恰好为
,则此时恰好只有重力作为它的向心力,杆和球之间没有作用力,如果速度不等于
,杆对小球的弹力就不为零,故B错误;
C、当v>
时,根据牛顿第二定律得:T+mg=m![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809697439.png)
当v由
逐渐增大时,T逐渐增大,故C错误;
D、当v<
时,根据牛顿第二定律得:mg-T=m![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809697439.png)
v由
逐渐减小时,杆对小球的弹力逐渐增大,故D正确.
B、小球在最高点时,如果速度恰好为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809619423.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809619423.png)
C、当v>
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809619423.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809697439.png)
当v由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809619423.png)
D、当v<
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809619423.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809697439.png)
v由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122809619423.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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