小船勻速逆流而上,經(jīng)過橋下時(shí)箱子落水了,船繼續(xù)前進(jìn)一段時(shí)間后才發(fā)現(xiàn),并立即調(diào)頭以相同的靜水船速順流而下,經(jīng)過1h在下游距橋7.2km處追上.則河水流動(dòng)速度為( ?。?br/>A. 7.2km/h
B. 1km/h
C. 3.6km/h
D. 條件不足,無法確定
河水與箱子是相對(duì)靜止的,船經(jīng)過橋下時(shí)箱子落水了,經(jīng)過1h在下游距橋7.2km處追上,說明1h箱子運(yùn)動(dòng)7.2km,也說明河水運(yùn)動(dòng)了7.2km,故河水的速度為:
v=
==7.2km/h故選:A.