A hockey goalie is standing on ice. Another player fires a puck (m = 0.170 kg) a

Question

A hockey goalie is standing on ice. Another player fires a puck (m = 0.170 kg) at the goalie with a velocity of +68.0 m/s.
(a) If the goalie catches the puck with his glove in a time of 5.91 x 10^-3 s, what is the magnitude of the average force exerted on the goalie by the puck?
(b) Instead of catching the puck, the goalie slaps it with his stick and returns the puck straight back to the player with a velocity of -68.0 m/s. The puck and stick are in contact for a time of 5.91 x 10^-3 s.
Now, what is the magnitude of the average force exerted on the goalie by the puck? Verify that your answers to parts (a) and (b) are consistent with the conclusion of Conceptual Example 3.

Explanation / Answer

Given Mass of the puck, m = 0.170 kg Initial velocity of the puck, vi = +68 m/s a) Time interval, dt = 5.91 *10^-3 s     From Newton's second law, F = dp / dt                            F = m (vf - vi) / dt                               = 0.170 kg (0 - 68 m/s) / (5.91 *10^-3 s)                            F = - 1956 N     Magnitude of the force is 1956 N b) In this case, the final velocity of the puck is, vf = - 68 m/s      Contact time interval, dt = 5.91 *10^-3 s                      F = dp / dt                      F = m (vf - vi) / dt                          = 0.170 kg (-68 - 68 m/s) / (5.91 *10^-3 s)                        F = - 3912 N Magnitude of the force is 3912 N                      F = m (vf - vi) / dt                          = 0.170 kg (-68 - 68 m/s) / (5.91 *10^-3 s)                        F = - 3912 N Magnitude of the force is 3912 N

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