A tennis ball is thrown up and reaches a height of 4.05 m before coming down. What was its initial velocity? (Assume g = 10 m/s2).

 For the upward motion of the ball, the final velocity of the ball (v) is given as 0. Now, if Distance travelled by the ball is 4.05 m, and acceleration a= – g = -10 m/s²

Apply Newton’s third equation of motion and get

v² = u² + 2 a s

0 = u² + 2 (-10) x 4.05

u² = 81

Then, u = 9 m/s T

Hence, the initial velocity of the ball is 9 m/s.