Question

How tall is a building if a stone dropped from its top in free-fall strikes the ground with a velocity of 40 m/s? assume that the original velocity is zero.

a. 78.2 m
b. 80.4 m
c. 79.8 m
d. 81.6 m

Answer 1

Vf = Vo + gt

Vo = 0

Vf = gt ==> t = Vf/g = 40m/s/9.8m/s^2 = 4.08 s

H = y - yo = Vot + 1/2 gt^2

H = 1/2 (9.8 m/s^2) (4.08s)^2 = 81.6 m

Answer: option d: 81.6 m