Solution :
In question it is given that —
Initial velocity, u = 0
Final velocity, v = ? (To be calculated)
Acceleration due to gravity, g = 9.8 m/s2 (Stone comes down)
And,
Height, h = 19.6 m
v2 = u2 + 2gh
v2 = (0)2 + 2 x 9.8 x 19.6
v2= 19.6 x 19.6
v2 = (19.6)2
v = 19.6 m/s
So, the velocity of stone just before hitting the ground will be 19.6 metres per second.