# Homework Help: Impulse that redirects a hockey puck 90°

1. Jan 5, 2014

### Daltohn

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

An ice hockey player receives a pass so that the puck, with a velocity of 18 m/s, glides across the ice, perpendicularly to the side axis (translation?) of the rink. After a slap shot, the puck moves exactly parallel to side axis of the rink, towards the goal with the velocity 33 m/s. Determine the impulse (magnitude and direction) of the hitting force the hockeystick affected the puck with. The mass of the puck is 170 g.
Answer: Imp=64 Ns , direction 29°.

Sorry for the awkward translation, I hope it is comprehensible!

2. Relevant equations

Imp=Δp

3. The attempt at a solution

So I take it you have to use the momentum, not Imp=FΔt, since you have all the needed quantities for it. I get the direction right, both the velocity and the momentum vectors are obviously perpendicular so I just use the tangent and get the angle. I have trouble with the magnitude of the impulse however. I understand you can't directly use the equation because of the different directions but I can't fit the impulse magnitude in with the above reasoning and the directions of the puck's momentums.

Any help is appreciated. :)

Last edited: Jan 5, 2014
2. Jan 5, 2014

### TSny

Hello, Daltohn, welcome to PF!

I believe that 64 Ns is not the right answer.

3. Jan 5, 2014

### Daltohn

Hi! My initial thought was to just use the Pythagorian theorem and calculate the magnitude of the vector, whose direction I had calculated to 28.6...°. I'm thinking that the impulse has to "cancel out" p1=0.17kg*18m/s, and also move give the puck p2=0.17kg*33m/s, in p2's direction. So Imp^2=3.06^2+5.61^2=40.83...→Imp=6.39...Ns.

4. Jan 5, 2014

### Daltohn

And that is very similar indeed to the "correct answer", which means they made a typo. :) Didn't realize!

5. Jan 5, 2014

### TSny

I think that's right.