posted by Jeff J. .
One can get a good idea of how deep a well is, for example, by dropping a rock and listening to how long it take to hear the rock as it hits the bottom. Suppose a rock was dropped into a well that was 410 meters deep and after the rock hits the bottom, a sound wave travels at a constant speed of 303 m/s upwards until it reaches your ears and you actually hear the rock. How long will it take, in seconds, to hear the rock from the moment it is dropped?
Figure the time to fall:
410=1/2 g t^2 solve for time
then figure time for sound to come up:
add the times.
As a practical matter, one can't hear the rock very well, it hits the sides going down, slows, bounces, so the entire process is not very accurate. I dispute that it is "good idea".