This question always comes up on many of our Range Rider runs when we stand gathered around an old vertical mine shaft staring into a black hole. Several people always have impressive answers, but no one is in agreement. Here is how you can easily approximate the depth of that mineshaft. The secret formula as I remember it from HS Physics is depth in feet = 1/2g x time², where g is the gravitational free fall acceleration of 32 feet/sec². To simplify, depth in feet = 16 x time². The time is the time in seconds for a rock you drop into the hole to hit bottom. For example if it takes one second the shaft is 16 ft deep. If it takes 2 seconds the shaft is 64 feet deep, 3 sec = 144 ft, 4 sec = 256 ft, 5 sec = 400 ft, 6 sec = 576 ft, 7 sec = 784 ft, 8 sec = 1024 ft, 9 sec = 1296 ft, and so on. In any case be very careful here, stand away from the edge and let the rock drop out of your fingers when performing this simple science experiment. 

Deadbear