题目内容
一石块A从80m高的地方自由下落,同时在地面正对着这石块,用40m/s的速度竖直向上抛出另一石块B,问:
(1)石块A相对B做什么方向,什么性质的运动?为什么?
(2)经多长时间两石块相遇?
(3)相遇时离地面有多高?
(4)石块A落地时,B运动的高度。(g取10m/s2)
(1)石块A相对B做什么方向,什么性质的运动?为什么?
(2)经多长时间两石块相遇?
(3)相遇时离地面有多高?
(4)石块A落地时,B运动的高度。(g取10m/s2)
(1) 石块A相对B向下做匀速直线运动,
,
(2)2s (3) 60m (4)80m
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162613051687.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162613192485.png)
试题分析:(1) 石块A相对B向下做匀速直线运动,速度大小为40m/s
设向下为正方向
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162613332812.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162613660725.png)
(2)以B为参考系,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626138001024.png)
(3)对于A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162613972838.png)
相遇时离地面的高度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162614299659.png)
(4)A落地时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162614580665.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162614736795.png)
对于B:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626150481058.png)
点评:解决本题的巧妙之处是以B为参考系,A以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162615329323.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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