Find the recoil velocity of a 65kg ice hockey goalie who catches a 0.15kg hockey puck slapped at him at a velocity of 50m/s. Assume that the goalie is at rest before catching the puck, and friction between the ice and the puck-goalie system is negligible. a. −0.12m/s
b. 0m/s
c. 0.12m/s
d. 7.5m/s

a. −0.12m/s

Explanation:

Given;

mass of the hockey goalie, m₁ = 65 kg

mass of the hockey puck, m₂ = 0.15 kg

velocity of the hockey puck, u₂ = 50 m/s

initial velocity of the hockey goalie, u₁ = 0

let the recoil velocity of the goalie = v

Apply Newton's third law of motion;

action and reaction are equal and opposite.

m₁v = -m₂u₂

65v = -(0.15 x 50)

65v = -7.5

v = - 7.5 / 65

v = -0.12 m/s

This shows that the goalie will move backwards with a velocity of 0.12 m/s.