题目内容
如图所示,质量m=10kg的木块在与竖直方向成370的力F的作用下沿竖直墙壁匀速上滑,已知木块与墙壁间的动摩擦因数μ=0.5,sin370=0.6,cos370=0.8,重力加速度g取10m/s2。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649714888.gif)
(1) F的大小?
(2) 若木块在F的作用下匀速下滑,则F又为多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649714888.gif)
(1) F的大小?
(2) 若木块在F的作用下匀速下滑,则F又为多大?
(1) 200N (2) 90.9N
(1)当木块匀速上升时,分析木块受
力如图。由平衡条件得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146497301176.gif)
①
②
③
联立①②③并代入数据解得:
④
(2)当木块匀速下滑时,分析木块受
力如图。由平衡条件得:
⑤
⑥
⑦
联立⑤⑥⑦并代入数据解得:
⑧
力如图。由平衡条件得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146497301176.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649745571.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649839491.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649855398.gif)
联立①②③并代入数据解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649870448.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146498861256.gif)
力如图。由平衡条件得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649901592.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649917530.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649933422.gif)
联立⑤⑥⑦并代入数据解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114649948484.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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