题目内容
如图AB轨道和一个半径为R的半圆弧相连,将一个质量为m的小球从距离水平面H=3R高处A点无初速的释放,整个过程摩擦力均可忽略,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242028338682700.png)
(1)小球到达B点的速度。
(2)小球到达C点时对轨道的压力。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242028338682700.png)
(1)小球到达B点的速度。
(2)小球到达C点时对轨道的压力。
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202835802616.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202834866631.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202835802616.png)
试题分析:(1)以地面为零势面,小球为研究对象
从A到B过程中:由机械能守恒定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202836816968.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202834866631.png)
从A到C过程:
由机械能守恒定律:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242028386421085.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202839687635.png)
在C点合外力充当向心力 即:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202840701899.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202841434553.png)
由牛顿第三定律得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202835802616.png)
点评:在使用机械能守恒解决问题时,关键要分清重力做功大小,以及物体动能始末状态
![](http://thumb2018.1010pic.com/images/loading.gif)
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