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I Directions of Impulse?

  1. Jul 27, 2017 #1
    This is in relation to a homework question: But I don't need assistance on the question itself, but the concept behind it.

    A mass of .4kg travels in the positive direction for 67m/s until a separate force is applied to M in the negative direction at 14m/s for .027 seconds. Impulse = 32.4 It then asks, "What is the average magnitude of the force?"

    I'm more confused on the wording - as to what is it asking specifically? Why is the force being asked to be represented as a magnitude when it should have direction as well?

    J = F Δt
    F= -32.4N*s/.027s

    Yet the answer states 1200N. Impulse should be negative, since it's coming in from the negative direction, right?

    What am I missing?
  2. jcsd
  3. Jul 27, 2017 #2
    It asks for the magnitude of the force, so therefore it would always be positive.

    You also seem to be confusing impulse and impact; the former is the change in momentum not the force applied.
  4. Jul 27, 2017 #3


    Staff: Mentor

    It probably should have been worded "magnitude of the average force"
  5. Jul 27, 2017 #4
    I don't follow. I calculated the change of time in there: J=FΔt.

    That makes more sense. I realized I calculated directions into it when it didn't ask for it.
  6. Jul 27, 2017 #5
    1200 Newtons is not the impulse; I'm not sure whether you thought it was or not.
  7. Jul 27, 2017 #6
    No no. Impulse was 32.4N*s in the negative direction. 1200N is the force.
  8. Jul 27, 2017 #7
    Oh, okay. It all seems good. :smile:
  9. Jul 29, 2017 #8
    Well, force consists of both a magnitude and a direction. You were already given the direction (the negative direction) so the only thing that's left to determine is the magnitude :).
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