题目内容
如图1-57(原图1-60)所示,将粗细均匀、直径相同的均匀棒A和B粘合在一起,并在粘合处用绳悬挂起来,恰好处于水平位置而平衡,如果A的密度是B的两倍,那么A的重力大小是B的_______倍.[5 ]
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144118111019.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241144118111019.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411858225.gif)
假设A的长度为x,B的长度为y,横截面积为S,B的密度为ρ,则A的密度为2ρ,有
,
,
根据力矩平衡条件得
,
代入得
,
所以
。
本题的正确答案为“
”。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411889504.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411904488.gif)
根据力矩平衡条件得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411904601.gif)
代入得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411936452.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411951905.gif)
本题的正确答案为“
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114411858225.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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