u = Initial velocity of the stone = 40 m/s
v = Final velocity of the stone = 0 m/s
s = Height of the stone
g = Acceleration due to gravity = −10 ms−2
Let h be the maximum height attained by the stone.
We know, v2 − u2 = 2gs
⇒ 02 − 402 = 2(−10)h
⇒ h = {40 \times 40 \over 20} = 80 m
Therefore, total distance covered by the stone during its upward and downward journey = 80 + 80 = 160 m
Net displacement during its upward and downward journey = 80 + (−80) = 0.