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Homework Help: Work out the velocity from the momentum?

  1. Oct 19, 2007 #1
    1. The problem statement, all variables and given/known data
    Does anyone know if it is possible to work out the velocity from the momentum?
    206Kg ms^-1 is the momentum... thanks

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 19, 2007 #2


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    do you have the mass?
  4. Oct 19, 2007 #3
    no i dont have the mass just the mometum
  5. Oct 19, 2007 #4


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    Then it's impossible to get the velocity... the velocity could be anything...

    momentum = mv
    v = momentum/m

    plug in difference m's and you get different v's...
  6. Oct 19, 2007 #5
    thanks for the formula.... if two skaters collide 1 has 75kg mass (180kg ms^-1 momentum) and the other has 60kg mass (100 kg ms^-1 momentum) than the total size of momentum before the collision would be 206 kg ms^-1 right? I want to calculate the velocity of 206kg ms^-1 thanks
  7. Oct 19, 2007 #6
    i made these mass's up
  8. Oct 19, 2007 #7


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    How do you get 206?

    you need to consider direction also... if they collide I assume they're going in opposite directions?

    Then if the momentum of the first is 180, and the other is 100 in the opposite direction... I'll call it -100 taking the direction of the 1st skater as positive...

    so total momentum = 180 + (-100) = 80kg*m/s

    So total momentum after the collision is also 80kgm/s by conservation of momentum.

    Now once they collide are they sticking together? Then using the definition of momentum and a total mass of 75kg+60kg... you can solve for the velocity using the momentum of 80kgm/s.
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