Mass of the ball is m = 15 kg
Velocity of the ball is v = 8 m/s
The momentum of the ball is
P = mv = (15 kg)*(8 m/s) = 120 (kg-m)/s
Because the ball rebounds elastically, its rebound velocity is 8 m/s in the opposite direction.
The change in momentum of the ball is
2P = 240 (kg-m)/s.
The impulse on the wall is equivalent to the change in the momentum of the ball, so it is 240 (kg-m)/s
Answer: 240 (kg-m)/s
