A warm hockey puck has a coefficient of restitution of 0.50, while a frozen hock

ID: 2117614 • Letter: A

Question

A warm hockey puck has a coefficient of restitution of 0.50, while a frozen hockey puck has

a coefficient of restitution of only 0.35. In the NHL, the pucks to be used in games are kept

frozen. During a game, the referee retrieves a puck from the cooler to restart play but is told by

the equipment manager that several warm pucks were just put into the cooler. To check to make

sure he has a game-ready puck, the referee drops the puck on its side from a height of 2 m. How

high should the puck bounce if it is a frozen puck?

answer: .25m

PLEASE PROVIDE WORKOUT STEPS

speed of the puck just before hitting groudn = sqrt ( 2*g*h) = sqrt ( 2*9.8*2) = 6.26099 m/sec

coeff of restituion = - ( v_ball - v_groung ) / ( u_ball - u_ground )

u_ball = intial velocity before colison = - 6.26099 m/sec

v_ball = final velocut of ball after collison

u_ground = intial speedof ground = 0

v_groung = fial peed of ground =

so v_ball = 2.19135 m/sec

now again ... v = sqrt ( 2*g*h)

so height h = v^2 . 2g = 2.19135^2 / (2*9.8) = 0.245 metres

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