Question

一列隊(duì)伍長(zhǎng)50米，行進(jìn)速度2.5m/s，經(jīng)過(guò)一座100m的涵洞，當(dāng)隊(duì)伍全部穿過(guò)涵洞時(shí)，總共需要（ ）
A．60s
B．40s
C．50s
D．80s

Answer 1

【答案】分析：當(dāng)隊(duì)伍全部穿過(guò)涵洞時(shí)，隊(duì)伍經(jīng)過(guò)的距離為隊(duì)伍的長(zhǎng)度與涵洞長(zhǎng)度之和，行進(jìn)速度已知，根據(jù)公式t=可求所需的時(shí)間．
解答：解：隊(duì)伍從隊(duì)首進(jìn)洞到隊(duì)尾離洞，一共行走的路程為S=S_隊(duì)+S_洞=50m+100m=150m，
當(dāng)隊(duì)伍全部穿過(guò)涵洞所需要的時(shí)間為t===60s．
故選A．
點(diǎn)評(píng)：本題考查時(shí)間的計(jì)算，關(guān)鍵是速度公式及其變形的靈活運(yùn)用，難點(diǎn)在于路程的確定，這也是本題的重點(diǎn)．