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Homework Help: Kinetic energy dissipation

  1. Nov 5, 2008 #1
    1. The problem statement, all variables and given/known data

    A hockey puck B rests on a smooth surface of ice and is struck by a second puck A , which was originally traveling at 40.0 m/s and which is deflected 30.0 degrees from its original direction. Puck B acquires a velocity at a 45.0 degree angle to the original direction of A . The pucks have the same mass.

    what fraction of the orignal kinetic energy of puck A dissipates during the collision.

    2. Relevant equations
    (Delta K) /K
    KE=0.5 mv^2

    3. The attempt at a solution
    i was able to solve for the velocity of both block a and b. But now i can't seem to figure out the original kinetic energy. I do not know where to go with the masses being the same.
    Va=29.3 m/s
  2. jcsd
  3. Nov 5, 2008 #2


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    You can express the kinetic energy in terms of the unknown mass "m", and go from there.
  4. Nov 5, 2008 #3
    (Kei-Kef)/ KEi = ((1-(m1/m1+m)) KEi)/KEI = M2/m1+M2 1/ (1+1) KE should be 0.5 or 50 percent. But this is the wrong answer And I'm Totally lost. thanks for any help that i may receive.
  5. Nov 6, 2008 #4
    I figured it out. 1-(KEf-KEi)/KEI is basically the equation to use.
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