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Homework Help: Center of mass

  1. Sep 15, 2007 #1
    1. The problem statement, all variables and given/known data
    A model airplane has a momentum given by
    [tex][(0.25 kg . m/s^3)t^2 - (0.75 kg . m/s^2)t]\hat{i}[/tex]
    a.) What are the x- , y- , and z- components of the net force on the airplane?
    b.) At what time t is the x-component of the net force on the airplane equal to zero?

    2. Relevant equations
    [tex]\sum F = \frac{d\vec{p}} {dt}[/tex]

    3. The attempt at a solution
    a.) i used the derivative to get :
    Fx = 2(0.25m/s^3)t - (0.75m/s^2) so the x- component of net force
    Fy = 0
    Fz = 0
    since they are the j hat and k hat where it is not given

    b.) when Fx = 0;
    0 = 2(0.25m/s^3)t - (0.75m/s^2)
    2(0.25m/s^3)t = (0.75m/s^2)
    t = 1.5s
  2. jcsd
  3. Sep 15, 2007 #2


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    Science Advisor

    Looks good to me!
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