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Homework Help: Calculate the impulse exerted after an inelastic collision

  1. Jul 17, 2016 #1
    1. The problem statement, all variables and given/known data
    A block A of mass m travelling with speed v collides head-on with a stationary body B of mass 2m. The two bodies stick together. Calculate the impulse exerted by body B on body A during the collision.

    2. Relevant equations
    ## J = p_{final} - p_{initial} ##
    ## p_{initial} = p_{final} ##

    3. The attempt at a solution
    I am not sure if this is correct. First I considered the system of the two blocks to calculate v':
    mv + 0 = 3mv' -> v' = v/3

    Then I calculated the initial and final momentum of block B on A using v' for final velocity:
    ## p_f - p_i = 2mv/3 - 0 = 2mv/3 ##

    But I don't feel confident in the answer.
  2. jcsd
  3. Jul 17, 2016 #2


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    Newton's third law of motion implies that the blocks should experience "equal but opposite" impulses during the collision. How does the impulse delivered to A compare to the impulse delivered to B in your solution?

    Does that boost confidence?
  4. Jul 17, 2016 #3
    It's -2mv/3, so it appears to be consistent. Thank you. Physics induces a great deal of uncertainty in me!
  5. Jul 17, 2016 #4


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    You're not alone. (I think Heisenberg said something similar.)
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