Momentum Hockey Puck Problem

Question

A 0.99 kg hockey puck is sliding along toward the defender at 5.05 m/s. The defender hits it back in the direction it came from, stick imparting a force of -132.9 N for 0.057 s. What is the final velocity of the puck? Please give your answer in m/s. Note: the force in negative because it is in the opposite direction of the puck's initial velocity. You may send a picture of your work for partial credit.

Answer 1

The Impulse-Momentum Theorem states that the Impulse is equal to the change in Momentum

Impulse = F•Δt

Change in Momentum = Final Momentum - Initial Momentum = p_f - p_i = mv_f - mv_i

Let's assume the puck is traveling from left to right. Since the force is negative, it will be acting in the opposite direction (right to left). If we call the force acting right-to-left as negative then the velocity acting left-to-right is positive:

F•Δt = mv_f - mv_i

F•Δt = m(v_f - v_i)

(-132.9)(0.057) = 0.99(v_f - 5.05)

-7.5753 = 0.99v_f - 4.995

-7.5753 + 4.995 = 0.99v_f

-2.5758 = 0.99v_f

v_f = - 2.6 m/s

In other words, the final velocity is 2.6 m/s in the direction of the force (away from the defender)