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Homework Help: Velocity and Collision Problem

  1. Jan 10, 2012 #1
    1. The problem statement, all variables and given/known data

    The first ball (A), of mass 0.5 Kg is rolled towards the second (B) at a velocity of 3.5 ms. Ball B then impacts ball C.

    Assume this collision is perfectly elastic.

    Calculate:
    a. The velocity at which ball A recoils after impacting with ball B.
    b. The velocity with which ball B collides with ball C
    c. The velocity with which ball B recoils from ball C
    d. The velocity at which ball C is moving after ball B has collided with i

    I don't know how to work this out! :/
     
  2. jcsd
  3. Jan 10, 2012 #2
    is there friction? as in is it actually rolling or sliding?
     
  4. Jan 10, 2012 #3
    Mass;

    Ball A = 0.5 kg
    Ball B = 0.782 kg
    Ball C = 0.386 kg

    No friction just that ball A is moving at 3.5ms on a flat surface
     
  5. Jan 10, 2012 #4
    do the collision between a and b first. total momentum before the impact equals the total momentum after, and the relative velocity after impact equals (-e)time relative velocity before impact. call initial velocities u1 and u2 and after collision v1 and v2

    so,
    m1u1+ m2u2 = m1v1 + m2v2

    and

    v2-v1 = -e(u2-u1)

    you know u1 and u2 as 3.5 and 0 and you also know m1 and m2 as 0.5 and 0.782

    just plug in the values and solve simultaneously
     
  6. Jan 10, 2012 #5
    Thanks, I'll try.. I've never done Physics before!
     
  7. Jan 11, 2012 #6
    The velocity at which ball A recoils after impacting with ball B

    -0.7698907956318254

    The velocity at which ball B collides with ball C

    2.7301092043681745

    The velocity at which ball B recoils from ball C

    0.9256192165494838

    The velocity at which ball C is moving after ball B has collided with it

    3.6557284209176584
     
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