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Homework Help: More impulse and restitution >.<

  1. Apr 9, 2004 #1
    God i hate this damned topic >.<

    Q. Two particles P and Q have speeds of 6m/s and 0m/s respectively. P directly collides with Q, the colision is perfectly elastic.

    a) find the speed of Q directly after impact
    b) find the impulse on Q

    so far i have worked out that using the law of conservation of momentum that

    6 = X + 0.5Y

    where x and y are the velocities of P and Q after the collision respectivly

    however this is as far as i have got because to work out n e thing more i would need the coefficient of restitution

    6 = E (X - Y)

    b) would be easy given the velocity after :P
  2. jcsd
  3. Apr 9, 2004 #2
    e=1 for perfectly elastic Collision
  4. Apr 9, 2004 #3
    perfectly elastic collision

    examples of a perfectly elastic collision (although they can never truly happen) would be a tennis ball that returns to its initial height after it is dropped or 2 billiards balls that collide and they exchange velocities. this should help get you started.
  5. Apr 9, 2004 #4


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    We would appreciate it if you would include ALL of the information in a problem (better: quote it exactly) rather than making us guess. I take it from "6= X+ 0.5Y" that P has mass 1 kg and Q has mass 0.5 kg but I don't see that information anywhere in the problem. Since this is a "perfectly elastic" collision, you also have conservation of kinetic energy (same thing: the "coefficient of restitution" is 1). Assuming P has mass 1 kg and Q has mass 1/2 kg then the total kinetic energy (1/2)(1)(62)= (1/2)(1)X2+ (1/2)(1/2)Y2 or 36= X2+ (1/2)Y2. That equation, together with X+ (1/2)Y= 6 is enough to solve for X and Y.
  6. Apr 9, 2004 #5

    sorry was sleepy wen i posted it

    thanks helped loads :)
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