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Inelastic Collision Scenario Question

  1. Sep 12, 2014 #1
    1. The problem statement, all variables and given/known data

    w1xtli.jpg

    A railway carriage with a mass m = 2.45×104 kg is initially travelling to the left with a speed Vi = 3.33 m/s. It collides and couples with (get stuck to) two identical railway carriages move to the left with a speed of Ui = 1.69 m/s.

    1. What is the speed of the railway carriage after the collision? (give a negative answer if the speed is to the right.)

    2. How much kinetic energy is lost in this collision?

    2. Relevant equations

    P = m1v1 + m2v2

    KE = 1/2mv2

    KE (before collision) = 1/2m1v12 + 1/2m2v22

    KE (after collision) = 1/2(m1+ m2)vf2

    3. The attempt at a solution

    1. P = (2.45×104 x 3.33) + 2(2.45×104 x 1.69)
    = 1.6x105 kgms-1

    ∴ P = 1.6x105 = (m1 + 2m2)vf = 7.35x104vf
    vf = (1.6x105) / (7.35x104)
    vf = 2.18 m/s

    2.
    KE (before collision) = 1/2m1v12 + 1/2m2v22
    KE (before collision) = 1/2(2.45×104 x (3.33)2) + 1/2(2(2.45×104 x (1.69)2)
    = 2.06x105 J

    KE (after collision) = 1/2(m1+ m2)vf2
    KE (after collision) = 1/2( 2.45×104+ 2(2.45×104) ) x (2.18)2
    = 1.75x105 J

    KE lost = 3.1x104 J

    Thank you for any help :)
     
  2. jcsd
  3. Sep 12, 2014 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    That's what I get.
     
  4. Sep 12, 2014 #3
    So I assume my working out and answers are correct?
     
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