题目内容
(10分)一个物块放置在粗糙程度均匀的水平地面上,受到水平拉力F作用,F随时间t变化的关系如图(a)所示,物块速度
随时间t变化的关系如图(b)所示.(g取10m/s2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241503346614720.jpg)
求:(1)1s末物块所受摩擦力的大小
;
(2)物块与水平地面间的动摩擦因数.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334536265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241503346614720.jpg)
求:(1)1s末物块所受摩擦力的大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334676326.png)
(2)物块与水平地面间的动摩擦因数.
(1)4N(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334754449.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334754449.png)
试题分析:(1)从图(a)中可以读出,当t=1s时,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334817638.png)
(2)从图(b)中可以看出,当t=2s至t=4s过程中,物块做匀加速运动,加速度大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334941912.png)
由牛顿第二定律得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150335035716.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150335113709.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150335222570.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150334754449.png)
点评:在解题过程中,对于t2=2s至t3=4s过程中,也可以运用动能定理求解质量.
![](http://thumb2018.1010pic.com/images/loading.gif)
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