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Center of mass and velocity problem

  1. Oct 30, 2006 #1
    If a particle of mass 5.30 kg is moving east at 10.0 m/s and a particle of mass 18.0 kg is moving west at 10.0 m/s, what is the velocity of the center of mass of the pair?

    I used the equation
    Vcm = P/M
    Vcm = [(5.70)(10) + (15)(10)] / [(5.70)+(15)]
    Vcm = 10 ms

    however, it says that is not the correct answer.
    I don't understand why. can someone help?
  2. jcsd
  3. Oct 30, 2006 #2
    Re-write your equation with units. Does everything work out? Are you putting the right numbers in the right places? It's hard to tell without units. Are all your signs correct?
  4. Oct 30, 2006 #3
    Vcm = P/M where P is (mass kg)(velocity m/s) and where M is the total mass (kg)

    Vcm = [(5.70kg)(10m/s) + (15kg)(10m/s)] / [(5.70kg)+(15kg)]
    Vcm = 10 m/s

    I'm still getting it wrong.
  5. Oct 30, 2006 #4


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    Homework Helper

    You seem to have put 5.7 kg instead of 5.3 kg and 15 kg instead of 18 kg.
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