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Collisions and Impulse

  1. Jul 12, 2010 #1
    1. The problem statement, all variables and given/known data

    Daisy (65.0kg) skates on ice at 4.5m/s to greet her friend (75.0kg), who is standing still, with open arms. As they collide, while holding each other, with what speed do the both move off together?


    2. Relevant equations

    MaVa+MbVb / Ma+Mb


    3. The attempt at a solution

    Is this correct?

    (Va+b)=75(0)+(65)(4.5) / 75+65
    = 0+69.5 / 140
    = .496m/s
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jul 12, 2010 #2
    using the equation

    m1v1 + m2v2 = (m1 + m2)vf

    I think you forgot to multiply the speed of Daisy to her mass.
     
  4. Jul 12, 2010 #3
    (65)(4.5)=/=69.5
    Multiplication not addition.
     
  5. Jul 12, 2010 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Careful with parentheses. This should be: (MaVa+MbVb) / (Ma+Mb)

    Redo your calculation.
     
  6. Jul 12, 2010 #5
    So I got (75(0) + 65(4.5)) / (75+65)
    = 0+292.5 / 140
    = 2.1 m/s
     
  7. Jul 12, 2010 #6
    that's correct :biggrin:
     
  8. Jul 12, 2010 #7
    thank you so much!
     
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