题目内容
分如图所示,在水平地面上有一个长L=1.5m,高h = 0.8m的长方体木箱,其质量为M=1kg,与地面间的动摩擦因数μ=0.3。在它的上表面的左端放有一质量为m= 4kg的小铁块,铁块与木箱间的摩擦不计。开始它们均静止。现对木箱施加一水平向左的恒力F=27N。(g=10m/s2)求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250034421801441.png)
(1)经过多长时间铁块从木箱上滑落?
(2)铁块滑落前后木箱的加速度
与
大小之比。
(3)铁块着地时与木箱右端的水平距离S。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250034421801441.png)
(1)经过多长时间铁块从木箱上滑落?
(2)铁块滑落前后木箱的加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442196310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442211341.png)
(3)铁块着地时与木箱右端的水平距离S。
(1) t=0.5s;(2)
=
;(3)4.32m
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442227417.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442242339.png)
试题分析: (1)铁块没有离开时,木箱在运动的过程中,铁块m相对于地不动,根据牛顿第二定律得,木箱的加速度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250034422741055.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442289559.png)
(2) 铁块离开时,木箱的速度v=at=6m/s.离开后,木箱的加速度a2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442305722.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442227417.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442352449.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442242339.png)
铁块离开时,铁块做自由落体运动,铁块落地的时间t2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442414587.png)
则铁块着地时与木箱右端的水平距离s=vt2+
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003442430597.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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