题目内容
(10分)如图所示,轻杆BC的C点用光滑铰链与墙壁固定,杆的B点通过水平细绳AB使杆与竖直墙壁保持30°的夹角.在B点悬挂一个不计重力的定滑轮,某人通过滑轮匀速的提起重物.已知∠CBO=60°,重物的质量m=45kg,人的质量M=60kg,g取10m/s2.试求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016160603883.jpg)
(1)此时地面对人的支持力的大小;
(2)轻杆BC所受力的大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016160603883.jpg)
(1)此时地面对人的支持力的大小;
(2)轻杆BC所受力的大小
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616107554.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616076593.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616107554.png)
试题分析:(1)对重物m由力的平衡条件得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616122557.png)
对滑轮受力分析可知,轻绳与竖直方向成
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616138397.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016161691005.png)
代入数值,解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616076593.png)
(2)定滑轮对B点的拉力F="2mg" cos30°,方向与竖直成cos30°夹角 2分
杆对B点的弹力方向沿杆的方向,由共点力平衡条件得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001616200938.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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