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Gliding on a skateboard

  1. Oct 31, 2004 #1
    Matt is gliding on his skateboard at 4.00 m/s. He suddenly jumps backward off the skateboard, kicking the skateboard forward at 8.00 m/s. Matt's mass is 50 kg and the skateboard's mass is 7 kg. How fast is Matt going as his feet hit the ground?

    This what I did:
    P_f = P_i

    v_f(50kg + 7kg) = 50kg*4m/s + 7kg*4m/s
    v_f = 4.49m/s ?
  2. jcsd
  3. Oct 31, 2004 #2
    Hmmm, not sure what you did.
    The initial momentum you calculated looks correct: (50+7)*4. But the total final momentum is Vf*50+7*8, where vf is the speed of Matt. Solving for Vf, I get 3.44 m/s. I'm probably wrong though.
  4. Oct 31, 2004 #3

    Doc Al

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    Staff: Mentor

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