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Homework Help: Momentum, elastically collisino, velocity

  1. Nov 5, 2009 #1
    1. The problem statement, all variables and given/known data

    A 0.200-kg mass is attached of a 0.800 m length string to form a pendulum. The pendulum is released from a horizontal position. At the bottom of its swing, it collides elastically with a 0.400-kg mass which is at rest on a horizontal, frictionless v surface. Find the velocity of each mass immidately after the collision.

    2. Relevant equations

    3. The attempt at a solution
    the answers are
    v .2kg= -1.32m/s
    v .4kg= 2.64m/s

    but I need to know the steps so I can study for the tests.
  2. jcsd
  3. Nov 5, 2009 #2


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    Homework Helper

    When the mass is released from its initial position, what is its velocity at the bottom of the swing? (Use the conservation of energy to find this.) Then use the conservation of momentum and energy to find the velocities.
  4. Nov 5, 2009 #3
    bottom of swing velocity = 3.96m/s(if I did right)

    x y are the velocities, not sure how to do next now.
  5. Nov 5, 2009 #4
    Je suis allé en France
    J'étais à la banque quand
    J'avais peur des chiens
  6. Nov 6, 2009 #5


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    Use law of conservation of energy.
    1/2*m1v1i^2 = 1/2*m1*Vf1^2 + 1/2*m2*v2f^2-------(1)
    According to conservation of momentum
    m1v1i = m1v1f + m2v2f-----------(2)
    From these two equations find v1f and v2f.
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