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Unit-vector momentum?

  1. Feb 1, 2009 #1
    [Resolved] Unit-vector momentum?

    1. The problem statement, all variables and given/known data
    A 0.200 kg ball hits a wall with a velocity of (7.60 m/s)i + (8.60 m/s)j + (3.50 m/s)k. It rebounds from the wall with a velocity of (1.80 m/s)i + (3.40 m/s)j + (-4.70 m/s)k. In unit-vector notation, what are (a) the change in the ball's momentum, (b) the impulse on the ball, and (c) the impulse on the wall?

    2. Relevant equations

    3. The attempt at a solution
    I attempted subtracting each component of the vectors multiplied by the mass, like this:
    Pi = ((7.6)-(1.8))*0.2
    Pj = ((8.6)-(3.4))*0.2
    Pk = ((3.5)+(4.7))*0.2


    This was wrong, and I'm not sure why it is or how to go about it. I submit with the wileyplus system, which said that none of my vector components were correct. Anyone know why?
    Last edited: Feb 1, 2009
  2. jcsd
  3. Feb 1, 2009 #2


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    Homework Helper

    Your calculations are initial - final?
  4. Feb 1, 2009 #3
    That was it, thanks!
  5. Feb 1, 2009 #4


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    Homework Helper

    You solved it yourself.

    All you needed was a sign.
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