First, we must assume that the planet has no atmosphere, so there's no air resistance,
and the behavior of the rock is the result of gravity and nothing else.
The formula for the distance covered by anything that accelerates from rest is
D = (1/2) (acceleration) (time)²
In this problem, we're given the distance and the time, and we want to find the acceleration.
1 = (1/2 acceleration) x (0.4)²
0.4² = 0.16
1 = (1/2 times 0.16) (acceleration)
1 = 0.08 acceleration
Acceleration = 1/0.08 = 12.5 meters per second²
That's about 27% greater than Earth's gravity.
