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Elastic collision, frictionless surface

  1. Dec 2, 2008 #1
    1. The problem statement, all variables and given/known data
    Two air hocky pucks collide head-on elastically on a frictionless surface. The smaller puck has a mass of 0.050 kg and is moving to the right at 5.0 m/s while the larger puck has a mass of 0.10 kg and is moving to the left with a speed of 2.0 m/s. Find the velocity of each after the collision.

    2. Relevant equations
    M1V1+M2V2=M1V'1+M2V'2
    .5M1V1^2+.5M2V2^2=.5M1V'1^2+.5M2V'2^2

    3. The attempt at a solution
    I am pretty sure I must derive an equation from conservation of momentum and conservation of energy.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 2, 2008 #2

    LowlyPion

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    Homework Helper

    That would be the way to do it.

    Select a positive X direction and be careful of signs.

    Two equations, 2 unknowns.
     
  4. Dec 2, 2008 #3
    Cant anyone help me?
     
  5. Dec 2, 2008 #4
    ok, could you give me an idea of what first step I should take?
     
  6. Dec 2, 2008 #5
    first I take the conservation of momentum:
    M1V1+M2V2=M1V'1+M2V'2

    Then I solved for V'1

    V'1=(M1V1+M2V2-M2V'2)/M1
    Then I substituted this for V'1 in the original equation:
    M1V1+M2V2=M1[(M1V1+M2V2-M2V'2)/M1]+M2V'2

    so now the only unknown variable is V'2. I have little expierence deriving equations so I am not confident this is correct. though it certainly seems to be. to me anyways.
     
  7. Dec 2, 2008 #6

    LowlyPion

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    Homework Helper

    My first step would be to start plugging in the values and deriving the actual equations for this situation.

    With the equations in hand then solve for the 2 velocities in the usual manner.
     
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