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Homework Help: How do you find speed?

  1. Dec 7, 2008 #1
    1. The problem statement, all variables and given/known data

    A 0.105-kg hockey puck moving at 20 m/s is caught and held by a 77-kg goalie at rest. With what speed does the goalie slide on the ice?


    2. Relevant equations

    (Initial puck speed)(Puck mass)
    = (combined mass)*(final goalie velocity)

    3. The attempt at a solution
    (0)(0.105)=(77.105)(20)
    = 1542.1 m/s
     
  2. jcsd
  3. Dec 7, 2008 #2
    wesDOT is correct. Initial velocity of the puck should not be zero.

    To cross-post from the other thread about two cars colliding inelastically:

    m1 : mass of the puck
    v1 : initial velocity of the puck
    m2 : mass of the goalie
    v2 : initial velocity of the goalie
    v' : final velocity of the puck+goalie

    Hope this helped.
     
  4. Dec 7, 2008 #3
    oops, double posted. sorry. & that was correct, thanks!
     
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