题目内容
如图所示,A、B为同一水平线上的两个绕绳装置,转动A、B改变绳的长度,使光滑挂钩下的重物C缓慢上升。关于此过程绳上拉力大小变化,下列说法中正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008534401618.jpg)
A.不变 B.逐渐减小
C.逐渐增大 D.可能不变,也可能增大
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008534401618.jpg)
A.不变 B.逐渐减小
C.逐渐增大 D.可能不变,也可能增大
C
试题分析:物体受到两个拉力是同一根绳子绕过挂钩的两段绳子拉力,所以两个拉力大小相等,根据受力平衡,合力竖直向上大小等于重力,受力分析如下图。设绳子和竖直方向夹角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000853456297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000853472654.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000853487746.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000853456297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008535032149.jpg)
![](http://thumb2018.1010pic.com/images/loading.gif)
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