【導(dǎo)讀】擰不緊的水龍頭每秒鐘會(huì)滴下2滴水,每滴水約毫升。小明同學(xué)在洗手后,、在如圖所示的方格紙中,經(jīng)過(guò)線段AB外一點(diǎn)C,求購(gòu)買這兩種樹(shù)苗各多少棵?如圖4,點(diǎn)P沿線段AB自A點(diǎn)向B點(diǎn)以2厘米/秒運(yùn)動(dòng),點(diǎn)P出發(fā)2秒后,點(diǎn)Q沿線段BA自B點(diǎn)向A點(diǎn)以3厘米/秒運(yùn)動(dòng),問(wèn)再經(jīng)過(guò)幾秒后P、Q相距5cm?