What is the height of a building in meters if it takes a rock 3.8 seconds to drop from its roof

height = 70.756 m

Explanation:
To answer this question, we will use one of the equations of motion which is:
x = ut + 0.5at²
where:
x is the distance that we want to calculate
u is the initial velocity of the body = 0 (assuming the body starts from rest)
a is the acceleration due to gravity = 9.8 m/sec²
t is the time taken = 3.8 seconds

Substitute with the givens in the above equation to get the distance as follows:
x = ut + 0.5at²
x = 0(3.8) + 0.5(9.8)(3.8)²
x = 70.756 m

Hope this helps :)