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Homework Help: Final velocities from head elastic head on collisions

  1. Feb 2, 2015 #1
    1. The problem statement, all variables and given/known data
    Ball A with velocity +3.00 m/s collides with ball B with equal mass traveling at -2.00 m/s. What is the velocity of each ball after the collision.

    2. Relevant equations
    Not sure.

    3. The attempt at a solution
    I know that momentum is conserved because, but solving the conservation of momentum equation yields two unknowns. I also tried impulse-momentum theorem and conservation of kinetic energy, but I'm not sure how that will help. The answer is Ball has velocity -2.00 m/s and ball B has velocity +3.00 m/s. Is there a formula to actually solve for this because they don't give you either of the final velocities.
  2. jcsd
  3. Feb 2, 2015 #2
    How did you use the law of conservation of kinetic energy?
  4. Feb 2, 2015 #3
    If you can put one of the velocities of the balls after the collision in term of the other , you can solve this problem.
    And the law of conservation of kinetic energy would help you.
  5. Feb 2, 2015 #4
    Well in my book they gave me a formula for relative velocity which is V2f-V1f = -(V2i-V1i). And I have the initial velocities and which will leave me with two unknowns still. Do I have to relate this somehow to conservation of kinetic energy and solve simultaneous equations?
  6. Feb 2, 2015 #5
    Ahh I got it. Thank you!
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