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An inelastic collision?

  1. Mar 8, 2009 #1
    1. The problem statement, all variables and given/known data

    Two wooden blocks of mass 8 kg and 4 kg respectively approach
    each other from opposite directions on a smooth level surface at a
    relative speed of 16 m s^1 . After a head-on collision they separate
    at a relative speed of 6 m s^1 . The initial velocity of the 8 kg block
    was 7 m s -1 North. Find the velocity of
    (a) the 4 kg block immediately before the impact;
    (b) the 8 kg block immediately after the impact;
    (c) the 4 kg block immediately after the impact.

    2. Relevant equations

    F x delta T= delta P

    For an elastic collision
    va-vb = -(va'-vb')

    3. The attempt at a solution

    Part (a) is straightforward

    Part (b) appears awkward because the collision seems inelastic because
    the relative velocity after impact is different in magnitude to that before
    impact and doesn't follow the relationship:
    va-vb = -(va'-vb')

    Am I correct in assuming the collision to be inelastic?
    How does one approach a solution to problem (b)?

    Help and guidance gratefully received.
  2. jcsd
  3. Mar 8, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    By making full use of the given information (the relative velocity after the collision) and applicable conservation laws (what's conserved?).
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