when a stone is dropped down a well, the distance fallen is given by D=4.9t^2 meters where t is the time taken in seconds

Answer 1

That is true.

Answer 2

That is true if D is in meters and g = 9.81 m/s^2
h = Hi -(1/2) g t^2 = Hi - (9.81/2) t^2 = Hi -4.9 t^2
So what?