1. A hockey player passes the puck to a teammate who is not paying attention. Th

Question

1. A hockey player passes the puck to a teammate who is not paying attention. The puck manages to hit the teammate’s stick in an elastic collision. The 160 g puck’s initial speed is +22 mph before it collides with the 600.g hockey stick. a) What are the velocities of the puck and stick after the collision (in m/s and mph)? b) What is the average force of the stick on the puck during the .20 s collision? c) What is the average power output of the stick during the collision? d) How would the physics of the problem, and your answers, have changed if the teammate had been paying attention to catch the puck?

Explanation / Answer

mp =160 g , mh =600g , up = 22 mph=9.835 m/s , uh =0

From conservation of momentum

mpup +mh*uh = mp*vp+mhvh

(160*22) +0 = (160*vp)+(600*vh) ... (1)

160*22 = (160*v1) +(600*v2)

For elastic collision vh-vp = up -uh

vh - vp = 22 ..(2)

v2 -v1 =22

vp = -12.74 mph = -5.7 m/s

vh =9.263 mph =4.14 m/s

(b) t = 0.2 s

Fp = mp(vp-up)/t = 0.16(-5.7-9.835)/0.2 =-12.418 N

Fp = 12.428 N

(c) P = energy/time = K1 -K2/t

K1 -K2 =(1/2)mpup^2 -(1/2)mpvp^2 - (1/2) mhvh^2

=(0.5*0.16*9.835*9.835) -(0.5*0.16*5.7*5.7) -(0.5(0.5*0.6*4.14*4.14)

=2.568 J

P = 2.568/0.2 = 12.84 W

(d) Yes , velocity will be changed, But Force is same, power is also changed

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