physics
posted by tommy .
If you drop a stone into a well that is d = 128.0 m deep, how soon after you drop the stone will you hear it hit the bottom of the well?

g = acceleration = 9.8 m^s^2
z = height = zo  Vo t  (1/2)(9.8)t^2
z = final height = 128
zo = initial height = 0
Vo = starting velocity = 0
so
128 = 4.9 t^2
t^2 = 128/4.9
t = 5.11 seconds 
Since the sound still needs to travel back up the well, it will actually take longer than 5.11 seconds.
v=d/t
343=128/t
t=0.37
5.11+0.37=5.48 seconds.