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Homework Help: Total Momentum

  1. Apr 5, 2007 #1
    1. The problem statement, all variables and given/known data

    Two identical objects A and B of mass M move on a one-dimensional, horizontal air track. Object B initially moves to the right with speed V0. Object A initially moves to the right with speed 3V0, so that it collides with object B. Friction is negligble. Determine the total momentum of the system of the two objects. Express answers in terms of M and V0.

    2. Relevant equations


    3. The attempt at a solution

    I got an answer,but i would like verification that it's right.

    I did...

    Pa=(Ma)(Va) Pb=(Mb)(Vb)
    Pa=m(3V0) Pb=m(V0)

    Add them together....
    m(3V0) + m(V0)

    and get...:surprised

    2m + 4v0
  2. jcsd
  3. Apr 5, 2007 #2
    That is so wrong and you know it.
  4. Apr 5, 2007 #3
    No, I really don't. What's right?
  5. Apr 5, 2007 #4
    Don't you notice that the expression 2m + 4v0 is non-sense? If not, I suggest you go study some algebra.
  6. Apr 5, 2007 #5


    User Avatar
    Homework Helper

    You're OK up to that last step. 2m + 4v0 does not make any sense. You cannot separate out the variables like that.

    What's the answer to this:

    3x + x = ?

    If you understand that, you should see what the answer should be.
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