Question

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 ?

Answer 1

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 .