A rock is dropped into an abandoned mine and a splash is heard 2 s later. Assuming that it takes a negligible time for the sound to travel up the mine shaft, determine the depth of the shaft and how fast the rock was falling when it hit the water.

Answer 1

In other words how far did it fall in 2 seconds
I assume you are using the metric system and g = 9.81 m/s^2
h = (1/2) g t ^2 = 4.9 t^2 = 4.9 * 4

v = g t = 9.81 * 2 meters/second

in general:
if a = -9.81
v = Vi - 9.81 t
y = Yi + Vi t - 4.9 t^2
here y is 0, ground
Vi is 0, initial velocity
Yi is height, what we want to know