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M2 Question watch

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    Check out the attachment. I can pretty much do b) providing I got a), but my answer completely differs from a).

    Just so that u can do a) nice and quickly: take conservation of momentum to get V in terms of the two unknowns. Then use coefficient of restitution e = v/u and do a bit of substitution to get the two unknown speeds in terms of e and V.

    My answers are:
    Velocity of A (the ball with mass m) = V[1/3 - 2/(3e)]
    Velocity of B (the ball with mass 2m) = V/(3e) x [(1+e)]

    The correct answers in the book are:
    Velocity of A (the ball with mass m) = 1/3(1-2e)V
    Velocity of B (the ball with mass 2m) = 1/3(1+e)V

    I struggle to see why 'e' is not part of a denominator of a fraction for either velocities, and therefore getting a wrong answer for part a) and b)! Please help!
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    (Original post by ResidentEvil)
    Check out the attachment. I can pretty much do b) providing I got a), but my answer completely differs from a).

    Just so that u can do a) nice and quickly: take conservation of momentum to get V in terms of the two unknowns. Then use coefficient of restitution e = v/u and do a bit of substitution to get the two unknown speeds in terms of e and V.

    My answers are:
    Velocity of A (the ball with mass m) = V[1/3 - 2/(3e)]
    Velocity of B (the ball with mass 2m) = V/(3e) x [(1+e)]

    The correct answers in the book are:
    Velocity of A (the ball with mass m) = 1/3(1-2e)V
    Velocity of B (the ball with mass 2m) = 1/3(1+e)V

    I struggle to see why 'e' is not part of a denominator of a fraction for either velocities, and therefore getting a wrong answer for part a) and b)! Please help!
    Haven't done m2 for a while...but isn't the coefficient of restitution:

    e = (Vb-Va)/(Ua-Ub) ????????

    v=eu is only for collisions with a surface...like a wall..

    G
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    (Original post by gzftan)
    Haven't done m2 for a while...but isn't the coefficient of restitution:

    e = (Vb-Va)/(Ua-Ub) ????????

    v=eu is only for collisions with a surface...like a wall..

    G
    yeah but i just said "e=v/u" as a generalised form which is what its based on.
    In this situation u do do
    e = (Vb-Va)/(Ua-Ub) depending if those are the directions taken
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    Ok...i've only done Vb..but maybe that'll set you on your way with the question...

    CLM: mV = mVa + 2mVb => V = Va+2Vb (1)

    using e....

    e = (Vb-Va)/V

    Ve = Vb-Va => Va = Vb - Ve (2)

    Sub (2) into (1)

    V = (Vb-Ve)+2Vb

    V + Ve = 3Vb

    V(1+e) = 3Vb

    1/3(1+e)V = Vb

    Hope this helps

    G
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    duhhhh I AM SO STUPID!!!!. Thanks mate
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    (Original post by ResidentEvil)
    duhhhh I AM SO STUPID!!!!. Thanks mate
    No probs

    G
 
 
 
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