Question

一列隊(duì)伍長L=80m，行進(jìn)速度v=3.6km/h，為了傳達(dá)一個(gè)命令，通訊員從隊(duì)伍排尾跑步趕到隊(duì)伍排頭，其速度v^′=3m/s，然后又立即用跟隊(duì)伍行進(jìn)速度相同大小的速度返回排尾．
求：（1）通訊員從離開隊(duì)伍到重回到排尾共用多少時(shí)間？
（2）通訊員歸隊(duì)處跟離隊(duì)處相距多遠(yuǎn)？

Answer 1

（1）在通訊員從隊(duì)伍排尾跑步到隊(duì)伍排頭的過程中通訊員相對(duì)于隊(duì)伍的速度大小為V=v′-v=2m/s，故通訊員從隊(duì)伍排尾跑步到隊(duì)伍排頭所需的時(shí)間為t₁=

l

v

=40s
在通訊員從隊(duì)伍排頭跑步到隊(duì)伍排尾的過程中通訊員相對(duì)于隊(duì)伍的速度大小為V′=v'+v=2m/s，故通訊員從隊(duì)伍排頭跑步到隊(duì)伍排尾所需的時(shí)間為t₂=

l

V′

=40s
故通訊員從離開到重回排尾一共所需時(shí)間t=t₁+t₂=80s．
（2）通訊員歸隊(duì)處跟離隊(duì)處的距離即為隊(duì)伍這段時(shí)間運(yùn)動(dòng)的位移：x=vt=80m
答：（1）通訊員從離開隊(duì)伍到重回到排尾共用80s；（2）通訊員歸隊(duì)處跟離隊(duì)處相距80m