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Homework Help: Impulse Question

  1. Sep 27, 2008 #1
    1. The problem statement, all variables and given/known data
    Two particles A and B, of mass 0.3 kg and m kg respectively, are moving in opposite
    directions along the same straight horizontal line so that the particles collide directly.
    Immediately before the collision, the speeds of A and B are 8 m s–1 and 4 m s–1 respectively.
    In the collision the direction of motion of each particle is reversed and, immediately after
    the collision, the speed of each particle is 2 m s–1. Find:

    a) the magnitude of the impulse exerted by B on A in the collision

    2. Relevant equations

    I = m(v-u)

    3. The attempt at a solution

    How do i know what mass to use? the mass m or 0.3? Is there a rule?

    Thanks :)
  2. jcsd
  3. Sep 27, 2008 #2

    Gib Z

    User Avatar
    Homework Helper

    Well. I = Ft, and by Newtons Third law, the magnitudes of the Forces should be negatives of each other, and the time of contact is obviously the same for both. Also, due to the Conservation of Momentum, I, which is just change in momentum, but also be the same magnitude for both particles.

    So basically, really, it doesn't matter which you sub in because you are to get the same value, but since you don't actually know the value of m, putting that into the equation won't give an answer, though putting in 0.3 will.

    From the previous information, you should now be able to determine m.
  4. Sep 27, 2008 #3
    Ahh i can use either ball. I see :)

    I can get m easy.

    Thank you very much :)
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