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Homework Help: Momentum and collision

  1. Aug 5, 2011 #1
    1. a 1kg ball traverse a frictionless tube. the ball after falling through a height of 1.2m, strikes a1.5kg ball which initially at rest. find the velocities of the two balls, if the collision is perfectly elastic. V1= -0.97m/s V2= 3.88m/s

    2. i found out the initial velocity of 1kg ball
    mgh = 1/2mv^2
    1(9.81)1.2= 1/2(1)v^2
    v= 4.85m/s

    after that, i use mu+mu = mv+mv
    1(4.85)+ 1.5(0)= 1v +1.5v2

    after that, what should i do to get the answer???
    help me....please....
  2. jcsd
  3. Aug 5, 2011 #2


    User Avatar

    Staff: Mentor

    In a perfectly elastic collision KE is also conserved. This gives you a second equation in the two unknowns (velocities of the balls after collision).
  4. Aug 5, 2011 #3
    what u mean?
    but i use newton's law of restitution to get the answer.

    -4.85=v1-v2---------second equation
    and i finally get the answer.
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