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Change in momentum of a ball

  1. Jan 2, 2010 #1
    1. The problem statement, all variables and given/known data
    A ball is rolled into a wall and bounces back at the same speed, the change in momentum is?

    2. Relevant equations
    Ein = Eout

    3. The attempt at a solution
    I thought it was m(v) but I got it wrong (doing test corrections ATM)

    Note I'm having trouble editing, so I made a new thread, I am not trying to spam.
     
  2. jcsd
  3. Jan 2, 2010 #2

    rock.freak667

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    If the velocity before impact is v, what is the velocity after impact?

    (remember, velocity is a vector quantity, so direction is important)
     
  4. Jan 2, 2010 #3
    So it's be -mv... but there aren't any negative answers:
    I have
    0
    1.5
    .5
    2
    and what I answered MV (all above are times MV as well)
     
  5. Jan 2, 2010 #4

    rock.freak667

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    So momentum before is mv, and momentum after is -mv, so that change in momentum is ?
     
  6. Jan 2, 2010 #5
    2mv?
     
  7. Jan 2, 2010 #6

    rock.freak667

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    is that one of the answers?
     
  8. Jan 2, 2010 #7
    yes, the answers were:
    0mv
    1mv
    1.5mv
    .5mv
    2mv
     
  9. Jan 3, 2010 #8
    Just to note:

    The original velocity must have been negative. The initial momentum was [tex] P_1=-mv[/tex].
    Following the bounce, the final momentum is [tex] P_2=mv[/tex].
    Hence the positive answer: P2-P1=2mv
    Either way the magnitudes are the same.
     
  10. Jan 3, 2010 #9

    rock.freak667

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    Yes the magnitudes are the same, but it didn't have to be negative. It depends on the direction you choose as positive.
     
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