题目内容
将四块相同的坚固石块垒成圆弧形的石拱,其中第3、4块固定在地基上,第1、2块间的接触面是竖起的,每块石块的两个侧面间所夹的圆心角为30°,假设石块间的摩擦力可以忽略不计,则第l、2块石块间的作用力与第1、3块石块间的作用力二大小之比值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412563864914571.png)
A.
B.
c.
D.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125639117340.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412563864914571.png)
A.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125639024344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125639055459.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125639086425.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125639117340.png)
B
如图对第一个石块进行受力分析,由几何关系知:θ=600,所以有N12 :N13=sin60°=
;
故选B.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125639055459.png)
故选B.
![](http://thumb2018.1010pic.com/images/loading.gif)
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