题目内容
一个气球以4m/s的速度从地面匀速竖直上升,气球下悬挂着一个物体,气球上升到217m的高度时,悬挂物体的绳子断了,问从这时起
(1)物体经过多长时间落到地面?
(2)物体速度大小变成2m/s所用的时间?(g取10m/s2)
(1)物体经过多长时间落到地面?
(2)物体速度大小变成2m/s所用的时间?(g取10m/s2)
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164114905416.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164114561401.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164114905416.png)
试题分析:(1)以竖直向上为正
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164115310735.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164115653660.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164114561401.png)
(2)若2m/s竖直向上:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164116340621.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164116745705.png)
若2m/s竖直向下
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164117073665.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164117432761.png)
点评:注意竖直上抛运动可分为向上运动和向下运动两段进行分析,而向上和向下为互逆过程,即向上的匀减速运动可看作向下的匀加速运动;此类题目也可以对全程应用匀变速直线运动规律.
![](http://thumb2018.1010pic.com/images/loading.gif)
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