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Calculating the height after an elastic collision

  1. Jul 2, 2013 #1
    1. The problem statement, all variables and given/known data
    A ball of mass 100 g is projected straight up with a speed of 5 m/s from the floor. Another ball of mass 50 g is hung from the ceiling by a light string at a height of 1.00 m directly above the first ball, so that the projected ball collides elastically with it. Calculate the height above the floor to which the smaller ball will rise.

    2. Relevant equations
    1/2 M1V1i^2 = 1/2 M1V1f^2 + 1/2 M2V2f^2

    3. The attempt at a solution
    When I use the equation above it gives me two unknown variables V1f and V2f (after the collision). but I don't know what equation to use to figure out Δy.

    Attached Files:

  2. jcsd
  3. Jul 2, 2013 #2
    You're using conservation of energy. Energy is not the only thing conserved in elastic collisions. In fact, the thing I'm thinking of is conserved even in inelastic collisions.
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