题目内容
(12分)如图所示,物块A、B用一轻绳相连,A放在倾角 θ=37º的斜面上,B竖直悬挂并保持静止,连接A与滑轮的细绳与斜面平行.已知物块A的质量mA=20 kg,物块与斜面间的摩擦因数=0.5,求物块B的质量mB.的取值范围。(sin37º=0.60,cos37º=0.80)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250010240458589.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250010240458589.png)
4 kg≤mB.≤20 kg
试题分析:物体B处于二力平衡,绳子的弹力等于物体B的重力
(1)若B的重力较小,则物体A有沿斜面向下运动的趋势,临界状态是有沿斜面向上的最大静摩擦力,把最大静摩擦力视为等于滑动摩擦力,根据力的平衡条件有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024045853.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024061899.png)
最大静摩擦力为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024077528.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024092605.png)
(2)若B的重力较大,物体A有沿斜面向上运动的趋势,则有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024045853.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024123899.png)
最大静摩擦力为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024077528.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001024139673.png)
综合可得:4 kg≤mB.≤20 kg
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目