Final answer:
The total momentum of the system remains the same before and after the hockey puck is caught by the goalkeeper, owing to the conservation of momentum. Both the puck and goalkeeper have the same momentum after the catch because they move as a single system with a combined mass. However, because the goalkeeper's mass is so much larger, his final velocity (and hence momentum) will be extremely small but not zero.
Step-by-step explanation:
When a hockey puck with a mass of 0.16 kg traveling at 40 m/s is caught by a stationary goalkeeper with a mass of 120 kg, the total momentum of the system after the catch can be calculated using the principle of conservation of momentum. Assuming a closed system with no external forces, the total momentum before the catch is equal to the total momentum after the catch. Since momentum is a product of mass and velocity (p = m*v), prior to the catch, the puck's momentum is 0.16 kg * 40 m/s = 6.4 kg*m/s and the goalkeeper's momentum is 120 kg * 0 m/s = 0 kg*m/s. After the catch, the combined mass is 120.16 kg, so we set the total final momentum (which must be the same as initial, 6.4 kg*m/s) equal to the combined mass times the final velocity. Therefore, the final velocity of the goalkeeper and puck combined can be found, and since the mass of the goalkeeper is much greater, the velocity will be very small but non-zero. Both the puck and the goalkeeper will have the same momentum after the catch since they are moving together, and it will be equal to the initial momentum of the puck alone.