题目内容
运动场上4×800m接力赛已进入了白热化阶段,甲、乙两队都已经是最后一棒。甲队员健步如飞,最大速度达
=12m/s,乙队员也不甘落后奋力直追,可能是由于紧张,甲队员不小心将接力棒失落,回头拾起棒后,甲加速直追反超乙。现将甲的加速和减速过程都视为匀变速运动,且加速时的加速度大小
=2m/s2,减速时的加速度大小
=6m/s2,拾棒时的速度为零,不计棒脱手后的位移和拾棒动作所花的时间,问:(1)甲在返回拾棒过程中的最大速率为多少?
(2)甲因为拾棒而耽误了多少时间?
(3)若丢棒时甲领先乙△
=8m,而距离终点
=240m,乙的速度保持
=10m/s,通过计算分析甲能否赢得比赛?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222520298.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222536315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222536344.png)
(2)甲因为拾棒而耽误了多少时间?
(3)若丢棒时甲领先乙△
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222567266.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222583324.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222598330.png)
(1)6m/s(2)9s(3)甲能赢得比赛
试题分析:(1)丢棒后,甲先减速至零,其时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222598699.png)
位移
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222614806.png)
之后反向加速,再减速至零,设最大速度为vm,则有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222630900.png)
(2)返回拾棒过程的时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222645858.png)
再继续加速前进到达最大速度的过程中,其时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222661697.png)
位移
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222661886.png)
若是没丢棒,跑这段位移的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222692662.png)
故耽误的时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222692767.png)
(3) 从掉棒开始计时,甲到终点需要的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222708910.png)
乙到终点需要的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222739757.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222754323.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002222770333.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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