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Homework Help: Momentum concepts (help please)

  1. Sep 27, 2005 #1
    A car of mass 1348kg moving with a velocity of 26m/s collides with a car os mass 674kg moving with a velocity of 21m/s in the same direction. after they collide the 674kg car moves with a velocity of 5.25m/s

    What is the velocity of the 1348kg object?

    M1 = 1348kg
    M2 = 674kg
    V1 = 26ms-1
    V2 = 21 ms-1

    Ptotalbefore = P1before + P2before
    Ptotalbefore = m1before * V1before + m2before * V2before
    Ptotalbefore = 1348*26 + 674*21
    Ptotalbefore = 49202kgms-1

    Ptotalbefore = Ptotalafter
    Ptotalbefore = P1after + P2after
    49202 – (674*5.25) = P1after
    P1after = 45663.6
    P1after = m1after * V1after
    P1after = V1after
    V1after = 45663.6
    V1after = 33.88ms-1

    According to my answer car1 speeds up from 26m/s to 33.88m/s after the collision. im certain that is not right but cant see where i have gone wrong can any one help me please.

    Thanks in advance
    Last edited: Sep 27, 2005
  2. jcsd
  3. Sep 27, 2005 #2


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    Homework Helper

    Uhmmm, the problem itself does not make much sense.
    How come the 674 kg car moves with a velocity of 5.25 m / s after the collision??? (5.25 m / s < 21 m / s).
    Infact, after the collision, the 674 kg car should have a greater velocity than it had before the collision...
    Viet Dao,
  4. Sep 27, 2005 #3
    Your solution looks right, its the problem that doesnt make sense. When you get rear ended you don't slow down.
  5. Sep 27, 2005 #4

    Cheers people will have words at college tomorrow

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