题目内容
如图所示,人站在岸上通过定滑轮用绳牵引小船,若水的阻力恒定不变,则在船匀速靠岸的过程中( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241655102392014.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241655102392014.jpg)
A.绳的拉力不断增大 | B.小船受的浮力不断增大 |
C.绳的拉力不断减小 | D.小船受的浮力不断减小 |
AD
试题分析:对小船进行受力分析,如图,因为小船做匀速直线运动,所以小船处于平衡,设拉力与水平方向的夹角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165510411297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241655104422564.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165510458566.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165510660879.png)
船在匀速靠岸的过程中,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165510411297.png)
根据平衡方程①知,绳子的拉力增大,
根据平衡方程②知,拉力增大,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165511284468.png)
所以船的浮力减小.故AD正确,BC错误.
故选AD.
点评:解决本题的关键掌握共点力平衡,知道小船在做匀速直线运动时,所受合力为0,根据
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165510411297.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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