题目内容
如图所示,木板静止于水平地面上,在其最右端放一可视为质点的木块.已知木块的质量m=1kg,木板的质量M=4kg,长L=1m,木板上表面与物块、下表面与地面之间的动摩擦因数均为
.现用水平恒力F=28N拉木板,g取10m/s2,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519216916372.png)
(1)木块与木板的加速度a1、a2的大小;
(2)木块滑到木板左端所需的时间;
(3)在(2)的时间内,拉力F所做的功。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921629428.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519216916372.png)
(1)木块与木板的加速度a1、a2的大小;
(2)木块滑到木板左端所需的时间;
(3)在(2)的时间内,拉力F所做的功。
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921785614.png)
(2)1s (3)56J
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921785614.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921910610.png)
试题分析:(1)对木块:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921957625.png)
木块的加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921785614.png)
对木板:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519222061090.png)
木板的加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151921910610.png)
(2)木块和木板的位移差等于木板的长度
即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151922315819.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151922456379.png)
(3)木板的位移
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151922549753.png)
拉力做的功
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151922690647.png)
W=56J
点评:(1)求加速度要找物体的合外力,不能少分析了力(2)两物体位移差等于板长的时间(3)某个力做的功等于这个力与力的方向的位移的积。
![](http://thumb2018.1010pic.com/images/loading.gif)
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