We can use 3rd equation of motion to find the velocity of the stone just before it strikes the ground.
Height = S = 318 meters
Acceleration = a= 9.8 m/s²
Initial velocity = u = 0
Final velocity = v = ?
According to the 3rd equation of motion:
2aS = v² - u²
2(9.8)(318)=v²
v²=6232.8
⇒
v = 78.95 m/s
So, the velocity rounded of to nearest integer will be 79 meters per second.
Thus, C option is the correct answer
