题目内容
在广场游玩时,一小孩将一充有氢气的气球用细绳系于一个小石块上,并将小石块置于水平地面上,如图所示.若水平的风速逐渐增大(设空气密度不变),则下列说法中正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241542290182673.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241542290182673.jpg)
A.细绳的拉力逐渐增大 |
B.地面受到小石块的压力逐渐减小 |
C.小石块滑动前受到地面施加的摩擦力逐渐增大,滑动后受到的摩擦力不变 |
D.小石块有可能连同气球一起被吹离地面 |
AC
试题分析:A、设细绳和水平方向夹角为θ,对气球受力分析,受到重力mg、风的推力F、拉力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229033364.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229142444.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229361616.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229423902.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241542295011021.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229033364.png)
BC、再对气球和小石块整体受力分析,受总重力(M+m)g、地面支持力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229642411.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229142444.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229844375.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229938831.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154230172438.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154230281597.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229642411.png)
D、小石块受到的支持力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824154229938831.png)
故选AC
点评:本题要注意整体法和隔离法的运用,还要注意受力分析时每个力的方向。
![](http://thumb2018.1010pic.com/images/loading.gif)
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