An object is dropped off a building that us 144 feet tall. After how many seconds does the object hit the ground? (s = 16t^2)

Given

s=16t^2

where

s=distance in feet travelled (downwards) since airborne with zero vertical velocity and zero air-resistance

t=time in seconds after release

Here we're given

s=144 feet

=>

s=144=16t^2

=>

t^2=144/16=9

so

t=3

Ans. after 3 seconds, the object hits the ground 144 ft. below.