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Homework Help: Momentum Theory question Gr.12

  1. Feb 18, 2013 #1
    1. A student on a skateboard, with a combined mass of 78.2 kg, is moving east at 1.60 m/s. As he goes by, the student skilfully scoops his 6.4-kg backpack from the bench where he had left it. What will be the velocity of the student immediately after the pickup?

    Me solving
    momentum of student = momentum of student+bag
    78.2kg(1.60 m/s E)= 84.6kg( Velocity)

    Velocity=1.5 m/s (E)

    QUESTION- What I don't get is the theory behind this. How does the momentum of the student equal the momentum of student and bag? Please explain how this works.

    Attached Files:

  2. jcsd
  3. Feb 19, 2013 #2
    (ms×vs)+(mb×vb) = (ms+mb)v^2

    ms = Mass of student
    vs = Velocity of student
    mb = Mass of bag
    vb = Velocity of bag

    In writing;
    The sum of the initial momentum (p=mv) on both objects is equal to the final momentum, where the masses are combined.

    If you have objects moving on angles, you can find the (x,y) components of the velocity vectors to determine what occurs. x=[(v)cos(θ)], y=[(v)sin(θ)]
    Last edited: Feb 19, 2013
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