You drop a rock down a well that is 11.5 m deep. How long does it take the rock to hit the bottom of the well?

The acceleration of gravity depends on the distance from

the center of the Earth. We use 9.8 m/s² for any place that's

on the Earth's surface, or reasonably close. The 11.5 meters

down into the well certainly qualifies.

The formula we want is:

Distance of fall = (1/2) · (acceleration) · (time) ²

11.5 m = (1/2) (9.8 m/s²) (time) ²

Divide each side

by 4.9 m/s² : (11.5m) / (4.9 m/s²) = time²

2.347 sec² = time²

time = √ (2.347 sec²) = 1.53 seconds.