题目内容
长L=1.4m,高h=1.25m,质量M=30kg的木箱,在水平地面上滑行,木箱与地面间的动摩擦因数
。当木箱的速度
1.2m/s时,把一质量为
=20kg的铁块轻轻地放在木箱顶的前端(铁块视为质点),铁块与木箱间动摩擦因数
,问
(1)铁块在木箱上怎样运动?
(2)铁块会从木箱的哪一端滑下来?铁块的落地点距木箱的滑落端的水平距离是多少?(g=10m/s2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241231183643001.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118115324.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118115220.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118130204.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118146322.gif)
(1)铁块在木箱上怎样运动?
(2)铁块会从木箱的哪一端滑下来?铁块的落地点距木箱的滑落端的水平距离是多少?(g=10m/s2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241231183643001.jpg)
(1) 铁块在木箱向右做匀加速直线运动,
m/s2
(2) 对木箱:受到铁块和地面对它的摩擦力均水平向左,木箱向右做匀减速直线运动
由牛顿第二定律:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118380449.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412311839573.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118411734.gif)
木箱的加速度![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118427836.gif)
铁块会从木箱的左端滑落,设经过时间t1铁块从木箱上滑下来
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118442684.gif)
解得:t1=2s
此时,铁块的速度,
0.4m/s
木箱的速度,
m/s
铁块从木箱的左端滑落,做向右的平抛运动,设落地的时间为t2
根据平抛知识,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118661383.gif)
铁块滑落后,木箱做向右的匀减速直线运动,加速度
m/s2
木箱在时间t2内的位移大小![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118707567.gif)
则,铁块落地点距木箱的水平位移大小
=0.0875m
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118364495.gif)
(2) 对木箱:受到铁块和地面对它的摩擦力均水平向左,木箱向右做匀减速直线运动
由牛顿第二定律:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118380449.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412311839573.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118411734.gif)
木箱的加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118427836.gif)
铁块会从木箱的左端滑落,设经过时间t1铁块从木箱上滑下来
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118442684.gif)
解得:t1=2s
此时,铁块的速度,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118458393.gif)
木箱的速度,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118473516.gif)
铁块从木箱的左端滑落,做向右的平抛运动,设落地的时间为t2
根据平抛知识,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118661476.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118661383.gif)
铁块滑落后,木箱做向右的匀减速直线运动,加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118676489.gif)
木箱在时间t2内的位移大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118707567.gif)
则,铁块落地点距木箱的水平位移大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123118739286.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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