Question

A hockey puck with a mass of 0.16 kg travels at a velocity of 40 m/s toward a goalkeeper. The goalkeeper has a mass of 120 kg and is at rest. Assuming a closed system and that ice is a frictionless surface, find the total momentum of the goalkeeper and puck after the puck is caught by the goalkeeper. Then, in 3-4 sentences, identify the object with the greater momentum, the puck or the goalkeeper, after the puck is caught and explain your reasoning based on the mass, velocity, and momentum of both the puck and the goalkeeper.(4 points)

Answer 1

Initial momentum = 0.16 kg × 40 m/s = 6.4 kg·m/s, so the total momentum after the catch (conserved) is 6.4 kg·m/s.
The combined mass is 120.16 kg, so their common velocity after the catch is v = 6.4 / 120.16 ≈ 0.0533 m/s. After the catch the goalkeeper has the greater momentum: p_goalkeeper = 120 kg × 0.0533 m/s ≈ 6.39 kg·m/s while p_puck = 0.16 kg × 0.0533 m/s ≈ 0.0085 kg·m/s. Although the goalkeeper’s velocity is small, his much larger mass gives him far more momentum than the puck.