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Homework Help: Elastic collision in a pendulum

  1. Apr 24, 2008 #1
    Hello people. New here and i've got a problem here which i would appreciate some help with.

    Situation :
    A ball of mass 300g is attached to a massless string of 0.2m suspended at a 90 degree angle to another ball of mass 500g held by a massless string at length 0.2m.
    Imagine the ball A (0.3kg) is positioned next to ball B, which are equal except for masses. Ball A is moved in a quarter of a circle motion up 0.2m, keeping it's string straight. That is the case we are examening.
    The question is, what are the maximum heights ball A and B can attain after ball A is released collides with B?

    We assume that this is an insulated system, meaning 100 % conserved energy and momentum.

    Through PEi + KEi = PEf + KEf We achieve the velocity 1.98 m/s right before collision with ball B.

    The problem arises when the total KE for the system has to be distributed correctly between ball A and B post-collision. I've reached the point where the KEi = Va final + 5/3 Vb final

    How do you go about finding either one of the velocities? I know that the V of B will be greater than V of A since B has less than double the mass of A

    Appreciate your help!
  2. jcsd
  3. Apr 28, 2008 #2
    Use the formulas for an elastic collision.

    [tex]p_{before} = p_{after}[/tex]

    [tex]KE_{before} = KE_{after}[/tex]

    That will give you 2 equations with 2 unknowns.
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