A rock dropped on the moon will increase it's speed from 0 m/s to 8.15 m/s in about 5 seconds what is the acceleration of the rock

Using the formula:

a = (Vf - Vi) / t

Our initial velocity is 0 m/s, and our final velocity is 8.15 m/s, with a time period of 5 seconds:

a = (8.15 - 0.0) / 5

a = 1.63 m/s^2

If you know the acceleration due to gravity on the Moon, you can confirm this answer. The recorded gravitational acceleration on the Moon is 1.62 m/s^2.