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Homework Help: Simple collisions question

  1. Jan 12, 2008 #1
    [SOLVED] simple collisions question

    1. The problem statement, all variables and given/known data

    http://img180.imageshack.us/img180/1253/28157442gm4.jpg [Broken]

    2. Relevant equations


    3. The attempt at a solution


    Gravitational potential energy = kinetic energy

    this gives u


    = 0.815 metres

    In a closed system, total momentum is always conserved.


    Momentum before = momentum after

    momentum before :
    mass X velocity
    (80/100) kg X 4 m/s = 0.32kgm/s

    momentum after :
    mass X velocity
    ((80/100) X 3) kg X x = 0.32 kgm/s

    therefore x = 1.33 m/s

    Is that rite?

    and for c) :

    ah i get it now!!!
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 12, 2008 #2


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    All is fine up to the momentum calculations where you use (80/100) as the mass. This should be (80/1000) or (8/100). You seem to have the right value for the momentum though so thats probably just a typo. What did you get for part c?

    EDIT: Just noticed you've solved it.
  4. Jan 12, 2008 #3
    oh yes srry! for part c i got : 2.67 seconds is tht rite?
  5. Jan 12, 2008 #4


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    Looks fine to me.
  6. Jan 12, 2008 #5
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