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 .
