题目内容
如图3-5-6所示,半圆形支架BAD,两细绳OA和OB结于圆心O,下悬重为G的物体,使OA绳固定不动,将OB绳的B端沿半圆支架从水平位置逐渐移至竖直的位置C过程中,分析OA绳和OB绳所受的力大小如何变化?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204222791846.jpg)
图3-5-6
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204222791846.jpg)
图3-5-6
TA一直减小,TB先变小后增大.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204222952672.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204222952672.jpg)
因为绳结点O受重物的拉力T,所以才使OA绳和OB绳受力,因此将拉力T分解为TA、TB(如下图).OA绳固定,则TA的方向不变,在OB向上靠近OC的过程中,在B1、B2、B3三个位置,两绳受的力分别为
和
、
和
、
和
.从图形上看出,TA是一直逐渐变小,而TB却是先变小后增大,当OB和OA垂直时,Tb最小.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120422326394.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120422373405.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120422404405.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120422435419.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120422467408.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120422467423.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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