A rock, dropped from rest near the surface of an atmosphere-free planet, attains a speed of 20.0 m/s after falling 8.0 meters.
-How long would it take the object, falling from rest, to fall 16 m on this planet?
A)0.8 s
B)1.1 s
C)2.5 s
D)3.5 s
E)22 s

Question

Quizplus · Accepted Answer

We can use the equation:

d = 1/2(gt^2)

where 
d = distance fallen = 16 m
g = acceleration due to gravity = 9.81 m/s^2 (assumed to be constant)
t = time elapsed

Rearranging:

t = √(2d/g)

t = √(2(16 m)/(9.81 m/s^2))

t ≈ 1.1 s

Therefore, the answer is choice B.

A Rock, Dropped from Rest near the Surface of an Atmosphere-Free