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Change in momentum after hitting a wall

  1. Jun 10, 2013 #1
    1. The problem statement, all variables and given/known data

    32) The change in momentum, in kg m/s, that occurs when a 1.0 kg ball travelling at 4.0 m/s strikes a wall
    and bounces back at 2.0 m/s is
    A) 2.
    B) 4.
    C) 6.
    D) 8.
    Answer: C

    2. Relevant equations

    Momentum==Mass*Velocity

    3. The attempt at a solution

    I get A.

    Momentum1==1*4
    Momentum2==1*2

    Momentum1-Momentum2==2
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 10, 2013 #2

    lewando

    User Avatar
    Gold Member

    Consider the "sign" associated with the two velocities.
     
  4. Jun 10, 2013 #3
    What a dumb mistake! Thanks :)
     
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