题目内容
(10分)在水平地面上放一木板B,重力为G2=100N,再在木板上放一货箱A,重力为G1=500N,设货箱与木板、木板与地面的动摩擦因数μ均为0.5,先用绳子把货箱与墙拉紧,如图所示,已知sinθ=3/5,cosθ=4/5,然后在木板B上施一水平力F,想把木板从货箱下抽出来,F至少应为多大?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241435290931354.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241435290931354.png)
F=850N
物体A、B的受力图如图所示,由受力平衡知:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241435291561448.png)
对A:
……①
A:
……②
……③)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241435299981171.png)
对B:
……④
B:
……⑤
……⑥
由①~⑥知: F=850N
本题考查受力平衡问题,先以整体为研究对象受力分析,把不在坐标轴上的力分解后列方程解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241435291561448.png)
对A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824143529234675.png)
A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824143529343832.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824143529421587.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241435299981171.png)
对B:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824143530060656.png)
B:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824143530497728.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824143530591615.png)
由①~⑥知: F=850N
本题考查受力平衡问题,先以整体为研究对象受力分析,把不在坐标轴上的力分解后列方程解得
![](http://thumb2018.1010pic.com/images/loading.gif)
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