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Homework Help: More momentum

  1. Apr 5, 2006 #1
    A 5kg model vehicle travelling at 14 m/s experiences a rocket boost of 85N (in the direction of motion) for 20s. What is the resulting speed?

    I tried using:

    F = mv/t, but that didn't work out for me.

    85 = 5v/20
    85*20 = 5v
    1700/5 = v
    v = 340 m/s

    but, that's wrong... what am I doing incorrectly? thanks.

    edit: I guess you could consider impulse actually, heh... whoops
  2. jcsd
  3. Apr 5, 2006 #2

    v(t)=v_initial + a*t

    F=m*a ----> a=F/m
    Last edited: Apr 5, 2006
  4. Apr 6, 2006 #3


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    Gold Member

    In this case F*t = mVf - mVi, in other words, the Ft equals the change in momentum.
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