题目内容
如图所示,一小球质量为m,用长为L的悬线固定在O点,在悬点O的正下方L/2处有一颗钉子D。现将悬线拉直后,使小球从A点静止释放,当悬线碰到钉子后的瞬间,下列说法错误的是:[ ]
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241913555844746.jpg)
A.小球的线速度没有变化
B.小球的角速度突然增大到原来的2倍
C.小球的向心加速度突然增大到原来的2倍
D.悬线对小球的拉力突然增大到原来的2倍
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241913555844746.jpg)
A.小球的线速度没有变化
B.小球的角速度突然增大到原来的2倍
C.小球的向心加速度突然增大到原来的2倍
D.悬线对小球的拉力突然增大到原来的2倍
D
试题分析:当碰到钉子瞬间,小球到达最低点时线速度没有变化,故A正确.根据圆周运动知识得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191355615513.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191355849338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191356114546.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191355849338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191356785853.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191357191567.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191357456887.png)
原来:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241913577831031.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191355849338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241913583141035.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824191358548368.png)
让选错误的,故选D.
点评:本题中要注意细绳碰到钉子前后转动半径的变化,再由向心力公式分析绳子上的拉力变化.小球摆到最低点虽与钉子相碰,但没有能量的损失.
![](http://thumb2018.1010pic.com/images/loading.gif)
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