题目内容
如图所示,杆AB、BC及滑轮的重力、摩擦力均不计,人匀速地提起重物.
=300N,若人的体重为
=500N,此时人对地面的压力多大?因重物匀速提升使斜杆和横杆所受的力分别有多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156448711887.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644809954.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644855958.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156448711887.gif)
200N; 400
N ;![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644965482.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644871962.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644965482.gif)
对
受力分析知,连接人与
绳中张力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156453551383.gif)
=
=300N,
则地面对人的支持力
N=
=200N,
设斜杆和横杆所受力分别为
和
,作用在B点绳的拉力
=600N,
则由力的分解得
Nc=
=400
(N),
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644809954.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644809954.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156453551383.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115645370947.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644809954.gif)
则地面对人的支持力
N=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156454011010.gif)
设斜杆和横杆所受力分别为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115645417966.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115645433953.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156454481022.gif)
则由力的分解得
Nc=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156454641074.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115644871962.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156454791264.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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