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Homework Help: Hockey Stick Momentum problem

  1. Feb 28, 2010 #1
    1. The problem statement, all variables and given/known data
    Two 72.0 kg hockey players skating at 5.45 m/s collide and stick together. If the angle between their initial directions was 115[tex]^{o}[/tex], what is their speed after the collision?

    2. Relevant equations
    p = mv

    [tex]p_{i} = p_{f}[/tex]

    3. The attempt at a solution

    Here's my interpretation of the image;

    http://img696.imageshack.us/img696/1493/momentum.png [Broken]

    [tex]p_{ix} = p_{fx} = 0[/tex]

    [tex]p_{iy} = p_{fy}[/tex]

    [tex]m_{A}v_{A} + m_{B}v_{B} = (m_{AB})(v_{AB})[/tex]

    [tex](72)(5.45cos(32.5)) + (72)(5.45cos(32.5)) = 144v_{AB}[/tex]

    [tex]v_{AB} = 4.60 m/s[/tex]

    Am I correct?
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 28, 2010 #2


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    Homework Helper

    P*cosθ components of the two players get canceled according to the diagram given by you . Check the other components. Your calculation will be correct if you use θ = 57.5 degrees.
  4. Feb 28, 2010 #3
    Oh, so I need to use sin instead?
  5. Feb 28, 2010 #4


    User Avatar
    Homework Helper

    For your mentioned angle, yes.
  6. Feb 28, 2010 #5
    Ok, so the new answer is 2.93 m/s.

    Thanks for the help
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