A 67 kg soccer player jumps vertically upwards ad heads the 0.47 kg ball as descends vertically with a speed of 24m/s .If the player was moving upward with a speed of 4.0 m/s just before impact, what will be the speed of the ball immediately after the collision if the ball rebounds vertically upwards and the collision is elastic?

A.)____m/s

B.) If the ball is in contact with the player's head for 20ms, what is the average acceleration of the ball.(note that the force of gravity may be ignored during the brief collision time.)

B.)____m/s^2