Question

甲球从楼顶自由下落a m时，乙球从距楼顶向下b m处自由下落，两球恰好同时落地.则楼的高度是(    )

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

Answer 1

C

解析：由自由落体运动的位移公式得：

a=gt₁²                                                                   ①

得甲比乙早下落的时间t₁=

设楼高是h,对甲球又有：

h=gt²                                                                 ②

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

得：t=                                                             ④

将t₁=代入④式得

t=,代入②得h=m.