Question

甲球從樓頂自由下落a m時(shí)，乙球從距樓頂向下b m處自由下落，兩球恰好同時(shí)落地.則樓的高度是(    )

A.(a+b) m          B.m             C.m          D.m

Answer 1

C

解析：由自由落體運(yùn)動(dòng)的位移公式得：

a=gt₁²                                                                   ①

得甲比乙早下落的時(shí)間t₁=

設(shè)樓高是h,對(duì)甲球又有：

h=gt²                                                                 ②

對(duì)乙球有h-b=g(t-t₁)²                                                    ③

得：t=                                                             ④

將t₁=代入④式得

t=,代入②得h=m.