题目内容
(8分)放在水平地面上的木块A、B分别重40 N和60 N,它们与水平地面之间的动摩擦因数均为0.25;夹在A、B之间的轻弹簧被压缩了2 cm,弹簧的劲度系数为400 N/m。现用F=4 N的水平拉力作用在木块B上,如图所示,求力F作用后木块A、B所受摩擦力的大小.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241459278531785.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241459278531785.jpg)
12N
试题分析:根据胡克定律弹簧的弹力大小为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145927931661.png)
对A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145928040787.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145928133783.png)
又由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145928321675.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145928430727.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145928586749.png)
可知力F作用后A、B静止不动,且:
A受到的摩擦力为8N方向水平向右;
B受到的摩擦力为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145928711569.png)
点评:本题难度较小,求解摩擦力时首先要判断摩擦力的类型,对于静摩擦力要注意静摩擦力的取值范围,静摩擦力的方向也是可以变化的
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目