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Homework Help: Impulse that redirects a hockey puck 90°

  1. Jan 5, 2014 #1
    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


    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. jcsd
  3. Jan 5, 2014 #2


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    Hello, Daltohn, welcome to PF!

    Can you show more detail of your calculation and state the answer that you got?

    I believe that 64 Ns is not the right answer.
  4. Jan 5, 2014 #3
    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.
  5. Jan 5, 2014 #4
    And that is very similar indeed to the "correct answer", which means they made a typo. :) Didn't realize!
  6. Jan 5, 2014 #5


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    I think that's right.
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