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Homework Help: Calculate final velocity

  1. Apr 27, 2016 #1
    1. The problem statement, all variables and given/known data
    Two freight trains have a completely inelastic collision at a track crossing. Engine 1 has a mass of 1.4x10^4 kg and is initially travelling at 45 km/h [N].
    Engine 2 has a mass of 1.5x10^4 kg and is initially travelling at 53 km/h [W]. Calculate the final velocity.
    2. Relevant equations

    3. The attempt at a solution
    p^2=p1^2+ p2^2
    =(1.4x10^4)(12.5m/s)^2+ (1.5x10^4)(14.72m/s)^2

    The answer in the textbook is 9.7m/s. What am I doing wrong?
  2. jcsd
  3. Apr 27, 2016 #2
    I just realised my mistake, i forgot to divide it by both mass
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