题目内容
两个可视为质点的小球a和b,用质量可忽略的刚性细杆相连,放置在一个光滑的半球面内,如图所示。已知小球a和b的质量之比为
,细杆长度、是球面半径的
倍。两球处于平衡状态时,细杆与水平面的夹角θ是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241139316667500.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931603218.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931634217.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241139316667500.gif)
A.45° | B.30° | C.22.5° | D.15° |
D
由题目中的数据可以得出,abO三点组成一个等腰直角三角形。所以两底角都为
。对两球进行受力分析,由于球面光滑,所以两球都只受到3个力,如图所示:重力、球面的支持力、刚性细杆的弹力。由于是刚性细杆,所以刚性细杆对两球的弹力均沿着杆方向,且对两球的弹力大小相等。两球处于平衡状态是,两球受到的合力都为零。两球受到的三个力都组成一个封闭的力的矢量三角形。再由正弦定理列出等式。对球
:
,对球
:
,所以:
,即
,所以
。答案D正确。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241139318372154.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931666227.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931681192.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931697878.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931744197.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931775825.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931790779.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931806608.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113931822288.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241139318372154.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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