A rock tumbles straight down from a cliff, it is moving at 20 m/s when it hits. What is the height of the cliff? The mass of the rock is 8 kg. A. 400 m
B. 160 m
C. 2.5 m
D. 20.4 m

D. 20.4m

Explanation:

assuming there is no initial velocity, where v=final velocity, g=acceleration due to gravity, and t=time

v = g*t

20 = 9.8*t

t =2.03 s

y = (1/2) g t^2  where y=vertical distance, g=acceleration due to gravity, and t=time

y = 4.9 (2.03)^2

y = 20.4 meters

the force on the thing and the distance the force moves the thing