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Homework Help: Impulse & Inelastic Collision

  1. Mar 29, 2009 #1
    1. The problem statement, all variables and given/known data
    Block A (2.1kg) is moving at 7.8 m/s to the right and collides head on with block B (3.4kg), which is moving at 4.2 m/s to the left.

    a) What is the velocity (magnitude and direction) of the blocks after the collision, if the two blocks stick together?

    b) What is the impulse (magnitude and direction) of block B on block A during the collision?

    2. Relevant equations
    m1v1 + m2v2 = (m1 +m2)(vf)

    3. The attempt at a solution
    a)I plugged in known values ((2.1)(7.8)+(3.4)(-4.2))=(5.5)vf
    vf=0.382 to the right, since the number was positive

    b)I'm not sure where to start.
  2. jcsd
  3. Mar 29, 2009 #2


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    Maybe start with what you know impulse is?
  4. Mar 29, 2009 #3
    J=delta p

    I wasn't sure where to start because I'm dealing with two objects moving at different speeds. I think I'm suppose to be dealing with initial and final velocities, however I don't know which initial velocity I would use since this is an inelastic collision.
  5. Mar 29, 2009 #4


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    But they ask you what the impulse is on Block A. You know its initial p. And since matter wasn't destroyed that same mass of A now has acquired a final velocity, and hence has experienced a Δ in p right?
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