题目内容
如图所示,在水平面上有一质量为M的长木板,开始时长木板上有一质量为m的小铁块(视为质点)以相对地面的大小为V0 的初速度从长木板的中点沿长木板向左滑动,同时长木板在沿水平向右的拉力F作用下始终以大小为V的速度作匀速运动(V >V0),小铁块最终跟长木板一起向右做匀速运动。已知小铁块与木板,木板与水平面间的摩擦因数均为μ,试问:
(1)小铁块从中点开始运动到最终匀速运动过程中水平拉力F的大小为多少?
(2)长木板至少为多长?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241226224783719.jpg)
(1)小铁块从中点开始运动到最终匀速运动过程中水平拉力F的大小为多少?
(2)长木板至少为多长?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241226224783719.jpg)
解:(1)如图M的匀速运动时有
F=μ·(M+m)g+μ·mg
F=" " μ·(M+2m)g
(2)设木板长为L,m滑行加速度大小为a,则a=
≥v·t-![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622525448.gif)
t=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622572298.gif)
联立得L≥![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622603526.gif)
F=μ·(M+m)g+μ·mg
F=" " μ·(M+2m)g
(2)设木板长为L,m滑行加速度大小为a,则a=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622510227.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622510234.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622525448.gif)
t=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622572298.gif)
联立得L≥
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122622603526.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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