Question

It takes 6 seconds for a stone to fall to the bottom of a mine shaft. how deep is the shaft

Answer 1

You need the kinematic equation for distance as a function of acceleration:

$d = [v(initial) *t] + 0.5a*t^{2}$

where a = gravitational acceleration 9.8m/s^{2}
v(initial) = starting velocity
t = time of fall

if the stone started at rest then v(initial) = 0 making the equation simply $0.5a * t^{2}$

Let me know if you still need further help :)