# Homework Help: Hockey question

1. Nov 13, 2009

### rpullo

1. The problem statement, all variables and given/known data

"Rockey Bourchard" sends a 0.4 kg puck at 80 m/s which is caught by goalie "Crazy Chretien" who is stationary on his knees on the ice. If the coefficient of friction of Chretien on the ice is 0.05, and his total mass is 90 kg, how far does he slide on the ice before coming to a stop?

2. Relevant equations

mv = mv' (conservation of momentum)
W = (delta)Ek

3. The attempt at a solution

Alright guys, I was just wondering if you can confirm this as the proper solution.
So first I found the momentum of the puck:

p = mv = (0.4kg)(80m/s) = 32 kg m/s

Since momentum is conserved, we can find the speed of the puck as it hits Chretien

v = p'/m = (32 kg m/s)/(90 kg) = 0.3556 m/s

With the equation "W = (delta)Ek"
I change it to " -F * d = 0.5mv2^2 - 0.5 m v1^2 "
and since v2 = 0 and the -F * d becomes ' μmgd', I got the equation
-μmgd = -0.5mv1^2

Solve for d:

d = (v1^2)/(2μg) = (0.3556 m/s)^2/(2*0.05*9.8m/s^2) = 0.13 m

2. Nov 13, 2009

### Delphi51

Looks good except that the mass of the hockey player holding the puck is 90.4 rather than 90.

3. Nov 13, 2009

### Andrew Mason

I am not sure why they are interested in the goalie. The puck is 2.5 times the weight of a normal hocky puck and moving twice as fast as the fastest NHL slapshot. So whoever shot this puck is the guy we should be interested in.:)

AM: