A ball is released from rest at a height of 15 metres above ground level. Find the speed of the ball when it hits the ground, assuming that no airresistance acts on the ball.

Expert Answers
justaguide eNotes educator| Certified Educator

The ball is released from a height of 15 m above ground level. It moves down due to the gravitational force of attraction of the Earth and the acceleration is 9.8 /s^2 in a vertically downwards direction.

If an object starting with an initial velocity u and a final velocity v travels a distance s at an acceleration a, v^2 - u^2 = 2*a*s

In the problem u = 0, v has to be determined, a = 9.8 and s = 15 m, substituting the values in v^2 - u^2 = 2*a*s

=> v^2 - 0 = 2*15*9.8

=> v^2 = 294

=> v = `sqrt 294`

=> v = 17.146 m/s

The speed of a ball that is dropped from a height of 15 m when it hits the ground is 17.146 m/s