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Momentum of two colliding trollies.

  1. Apr 3, 2013 #1
    The question is shown in the first image attached.

    I did three ways to solve it, and all three answers were wrong. After some trial and errors, I found the correct solution, which is written in the little box in the second image.

    However, I still find my three solutions reasonable. I used both Principle of Conservation of Momentum and Principle of Conservation of Energy. I substituted everything correctly too. Why are they wrong?
     

    Attached Files:

  2. jcsd
  3. Apr 3, 2013 #2
    Kinetic energy is not conserved here since it is an inelastic collision.
    For your first attempt, just use the first equation you've written down, remembering that mA = mB
     
  4. Apr 3, 2013 #3

    Doc Al

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    Staff: Mentor

    Mechanical energy is not conserved--the cars stick together. In fact, one of the questions asks for the fraction of KE lost.
     
  5. Apr 3, 2013 #4
    ap123, thank you.

    Is it possible for one of the trolley to transfer all of its kinetic energy to another trolley while still being able to stick together with it? I mean like, when the first trolley hits the other, in that fraction of a second before any sound energy could be produced, the second trolley just starts moving and kinetic energy is conserved?
     
  6. Apr 3, 2013 #5

    Doc Al

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    Staff: Mentor

    No, not if they stick together.
     
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