# Physics

Ice-hockey star Wayne Gretzky is skating at 12.7 m/s toward a defender, who in turn is skating at 5.39 m/s toward Gretzky. Gretzky’s weight is 677 N; that of the defender is 869 N. Immediately after the collision, Gretzky is moving at 2.21 m/s in his original direction. You can ignore external horizontal forces applied by the ice to the skaters during the collision. What is the velocity of the defender immediately after the collision?

Hint: Take Gretzky’s initial direction as the positive velocity.

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1. initial momentum in + x direction =
677/g * 12.7 - 869/g * 5.39
= +3914/g
final momentum in + x direction = 677/g * 2.21 + 869/g * V
= +1496/g + 869/g * V
so
3914 = 1496 + 869 * V
2418 = 869 V
V = + 2.78
Wayne Won

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