题目内容
如图所示,小球放在小车中的斜面A和竖直挡板B之间,所有接触面均光滑。起始小车向左匀速运动,某一时刻改为向左匀减速运动,整个过程中小球与小车处于相对静止状态。关于前后两个状态下斜面对小球的弹力的大小
和挡板对小球的弹力的大小
的变化,以下说法正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241251136852897.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125113607428.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125113654437.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241251136852897.png)
A.![]() ![]() | B.![]() ![]() |
C.![]() | D.![]() |
A
小球受重力,斜面对小球的弹力的大小
和挡板对小球的弹力的大小
,设斜面与水平面夹角为
,竖直方向
,不管是匀速运动还是匀减速运动,不改变竖直方向的平衡,故
不变,水平方向做匀速运动时:
,因为小车向左做匀减速运动,所以
减小
故选A
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125113607428.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125113654437.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125114059297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125114075780.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125113607428.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125114122720.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125113654437.png)
故选A
![](http://thumb2018.1010pic.com/images/loading.gif)
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