Refer to Conceptual Example 3 as an aid in understanding this problem. A hockey

Question

Refer to Conceptual Example 3 as an aid in understanding this problem. A hockey goalie is standing on ice. Another player fires a puck (m = 0.17 kg) at the goalie with a velocity of +68 m/s. (a) If the goalie catches the puck with his glove in a time of 5.90 10-3 s, what is the average force (magnitude and direction) 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 m/s. The puck and the stick are in contact for a time of 5.90 10-3 s. Now what is the average force exerted on the goalie by the puck?

Explanation / Answer

calculate the momentum before the puck hits the goalie: momentum = mass*velocity p = 0.17*54.9 p = 9.333 kg.m/s Because the final momentum is zero, the change in momentum is also 9.333, which is also called impulse. Apply impulse = Force*time 9.333 = 3.62*10^-3*F F = 2578.17679558 Therefore the average force exerted is 2578N b.) As we said from the previous question the original momentum is 9.333 kg.m/s. However, this time the final momentum is not zero: apply momentum = mass*velocity: p = 0.17*-54.9 p = -9.333 kg.m/s So this time the change in momentum is 9.333--9.333 = 18.666 kg.m/s, this is also the impulse. apply impulse = Force*time 18.666 = 3.62*10^-3*F F = 18.666 / 3.62*10^-3 F = 5156.35359116 So now the average force is 5156N Hope this helps

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