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Conservation of energy/momentum

  1. Apr 7, 2014 #1
    1. The problem statement, all variables and given/known data
    In a railroad accident, a boxcar weighing 200 kN and traveling at 3.00 m/s on a horizontal track slams into a stationary caboose weighing 400 kN. The collision connects the caboose to the boxcar. How much energy is transferred from kinetic energy to other forms of energy in the collision?


    2. Relevant equations
    KE= 1/2 m v^2
    P= mv


    3. The attempt at a solution
    KE initial= 1/2 (200000) (3)^2
    =900000 J
    P initial= 200000 (3)
    =600000 kg m/s

    I have no idea where to go from here
     
  2. jcsd
  3. Apr 7, 2014 #2
    Point 1: The mass of the boxcar is only about 20000 kg, not 200000 kg. Maybe 20400 kg.
    Point 2: The final momentum will NECESSARILY equal the initial momentum, and the final mass is necessarily 61200 kg, so the final velocity of the stuck-together mess is easy to find.
    Point 3: Once you have the final velocity, you can find the reduction in kinetic energy -- all of the reduction is "transferred to other forms of energy" - mainly heat, but possibly sound, etc.
     
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