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Homework Help: Collision Problem

  1. Jun 8, 2005 #1
    A 12 kg block (A) is sliding right with a speed of 2.2 m/s collides with a 20 kg block (B) which is travelling left at 3.0 m/s.

    After the collision the 12 Kg block is moving left at a speed of 1.6 m/s

    a) what is the velocity of the 20 kg block after the collision?

    b) The collision lasts for 0.025s, what is the average force experienced by the 12kg block?

    For a) i just used:

    P = mv

    Pa + Pb = Pa' + Pb'

    plugged in the numbers and got Vb' = .72 m/s left.

    I'm having trouble with part b) .. any ideas on how i could get started?

  2. jcsd
  3. Jun 8, 2005 #2
    For part B), you need to consider the relationship between impulse and momentum (in terms of forces).
  4. Jun 8, 2005 #3
    ok, well i know that impulse is the change in momentum.

    I could find the change in momentum by subtracting Pa' from Pa.

    So now I have the impulse

    How do I come up with the average force? or is the impulse itself the average force?
  5. Jun 8, 2005 #4
    Force is the change in momentum per unit time.
    Average force is the net change in momentum over the net change in time.
  6. Jun 8, 2005 #5
    man i have to learn how to use these markup codes....

    so I'm thinking that the average force can be found by using:

    F = (m /\V)/(/\t)

    Im using /\ for delta or "change in"
  7. Jun 8, 2005 #6
    That looks good to me.
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