Question

During a training session a footballer kicked a ball with a velocity of 14ms-1 and another footballer kicked a second ball of equal mass in the opposite direction with a velocity of 20ms-1. The two balls made a head on head collision and the first ball began to move with a velocity of 16ms-1 in the opposite direction find the new velocity of the second ball each ball is 900g

Answer 1

From the conservation of momentum:

$$mv_1-mu_1=-mv_2+mu_2$$

$$v_1-u_1=-v_2+u_2$$

$$14-20=-16+u_2$$

$$u_2=10\frac{m}{s}$$