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Inelastic collisions between two blocks

  1. Dec 13, 2011 #1
    1. The problem statement, all variables and given/known data

    A 2.0 kg block slides along a frictionless surface at 1.0 m/s. A second block, sliding at a faster 4.0 m/s, collides with the first from behind and sticks to it. The final velocity of the combined blocks is 2.0 m/s. What is the mass of the second block?

    2. Relevant equations

    law of conservation of momentum...

    m1u1 + m2u2 = m1v1 + m2v2

    3. The attempt at a solution

    (2 kg * 1 m/s ) + (m2 * 4 m/s) = (2kg + m2) 2.0 m/s

    2 J + (4 m/s m2) = 4 J + (2.0 m/s m2)

    4 m/s m2 = 2 J + (2.0 m/s m2)

    now I'm lost.....
     
  2. jcsd
  3. Dec 13, 2011 #2
    Just finish your algebra

    by the way kgm/sec is not joule, it's just kg m/sec, which is the same as N sec

    so you have the equivalent of

    4m = 2 + 2m

    subtracting 2m from both sides
    2m = 2

    m = 1kg
     
  4. Dec 13, 2011 #3
    Thanks netgypsy... now i feel like a true student. haha
     
  5. Dec 13, 2011 #4
    Good job!
     
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