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Linear Momentum

  1. Apr 11, 2004 #1
    Two balls hit eachother.

    One ball with a mass of 2m standing still relative to the earth. The other ball has a mass of 1m and hits the ball of 2m at a certain speed. The collision is elastic.

    Could you calculate the proportion of Linear Momentum between both balls after the collision with this information?
  2. jcsd
  3. Apr 11, 2004 #2
    M1 = 2m
    M2 = m
    v - speed before collision
    u - speed after collision

    [tex]M_1v_1 + M_2v_2 = M_1u_1 + M_2u_2[/tex]

    Cancelling the mass and zero speed we get:

    [tex]v_2 = 2u_1 + u_2[/tex]

    Second equation:

    [tex]\frac{1}{2}(M_1v_1^2 + M_2v_2^2) = \frac{1}{2}(M_1u_1^2 + M_2u_2^2)[/tex]

    Cancelling the mass and zero speed we get:

    [tex]v_2^2 = 2u_1^2 + u_2^2[/tex]

    Two equations with two variables, you can find both u1 and u2 and therefore the ratio of linear momentums of both balls. I think it turns out to be -1...

    (By the way, I assumed head-on collision here. If it's not you also need the angle.)
    Last edited: Apr 11, 2004
  4. Apr 11, 2004 #3
    Thanks!... it's actually not a head-on collision, but I figured out I could manage to fit in the angle myself. If I experience difficulties I'll let you know. :cool:
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