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Homework Help: Perfectly Inelastic

  1. Mar 11, 2009 #1
    Ball 1, with a mass of 100 g and traveling at 10 m/s, collides head-on with Ball 2, which has a mass of 300 g and is initially at rest. What are the final velocities of each ball if the collision is perfectly inelastic?

    We're suppose to be talking about Energy, but I figured I could use:

    mv+mv (initial)=mv (final)

    I got 2.5 m/s for both balls, because if the objects are inelastic they will be traveling at the same speed after collision and momentum is conserved.
    Is this right?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 11, 2009 #2


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    That would be correct.
  4. Mar 11, 2009 #3
    but now I just tried to use conservation of Energy and got a different answer. I tried
    1/2 mv^2 + 1/2 mv^2 = 1/2mv^2 (final for system)

    I got both balls traveling at 5 m/s ??
  5. Mar 11, 2009 #4


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    Kinetic energy is not conserved in an inelastic collision.
  6. Mar 12, 2009 #5
    I tried the V' substitution before but was wrong.

    The expression that the book describes it to be:
    ---> the square root of [(m+M)kd^2] / m^2
  7. Mar 13, 2009 #6
    You might want to find out the kinetic energy of the balls before the collision, because you are talking about a change in energy.
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