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Net force

  1. Sep 26, 2007 #1
    this was a question in my exam:
    A plane was ( just reconfirmed, it is acutally an IS)climbing steadily upwards with a velocity of 6ms^-1. What is the net force on a pasenger on the plane(not by the plane)?
    (a) mg
    (b) 6mg
    (d) something i dont remember but is a definite value

    i was debating with the teacher that it is 0 but she keeps saying mg
    so who is rite and how?
    Last edited: Sep 26, 2007
  2. jcsd
  3. Sep 26, 2007 #2
    A plane was climbing steadily upwards with that velocity? Which means that it isn't anymore, and is free falling (unlike an actual plane)?
  4. Sep 26, 2007 #3
    that is such a trick question!
  5. Sep 26, 2007 #4
    but if it IS climbing
    what is the answer
  6. Sep 26, 2007 #5
    More like a stupid, pointless question that tests your knowledge on nothing other than semantics.
  7. Sep 26, 2007 #6
    If the plane was climbing, at a constant velocity, there is no acceleration, and the forces on the place (thrust and gravity) sum to zero. Unless you are bouncing around in the plane, you have the same forces as the plane, after enough Newton's third law stuff, which sum to zero.
  8. Sep 26, 2007 #7

    This is the sort of dumb question that makes people hate physics. The teacher who gave this should have to spend the rest of his/her life answering questions like
    "A grandfather clock is in orbit over Cleveland. A mouse is running up the pendulum. It has a propeller beanie on its head. At 6:30 as the clock strikes, the mouse leaps. Describe the motion of the propeller tip."

    Anyway, the answer should be mg. Constant velocity flight doesn't affect your weight which is the force on you.
  9. Sep 26, 2007 #8

    Doc Al

    User Avatar

    Staff: Mentor

    If you've accurately presented the problem, I'd say you were right. If the velocity of the plane (and the passenger, of course) is constant then the net force on the passenger is zero.

    If she had worded it "The force of the passenger on the plane" (meaning: what force does a passenger exert on the plane) then that force would equal the weight of the passenger. But if that's what she meant to ask, she could have worded the problem more carefully.
  10. Sep 26, 2007 #9
    Mmm, I read that as meaning "not counting whatever the plane is doing". I see your point and I think this teacher asks very bad questions. This person is not in free-fall. I would be able to measure physiologic responses showing this person is subjected to a net force of approximately mg. To paraphrase Pauli, this question isn't even bad.
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