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Airplane and momentum

  1. Oct 30, 2006 #1
    You are on an airplane that is moving forward through the air? As you get up to move forward through the cabin to the restroom , what happens to the forward momentum of the pilot? (assume the plane and the passenger make up a closed system)

    a) it stays constant
    b) it increases
    c) it decreases
    d) there is no change as all forces exerted by the passenger are internal
    e) the internal forces caused by the passenger increase the momentum of the airplane

    My reasoning: the answer is that it increases because there is a force being pushed on the pilot from the passenger moving forward therefore the momentum is larger
  2. jcsd
  3. Oct 30, 2006 #2


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    Staff: Mentor

    But which way is that force being exerted on the pilot? Which way does the passenger push with his shoes to start his forward motion? How is the floor under the passenger connected to the pilot's seat?
  4. Oct 30, 2006 #3
    Think about it, visualize it, whatever else it. Draw yourself a force diagram and look at what happens to the airplane.

    EDIT: I hate when that happens. Berkeman and I posted at the same time :-p
  5. Oct 30, 2006 #4
    The passenger pushes his feet down then pulls back to move forward therefore it should decrease right?
  6. Oct 30, 2006 #5


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    Staff: Mentor

    Correct. The plane + passengers system has a constant total momentum, so if a passenger pushes himself forward, increasing his momentum, that happens at the expense of the momentum of the rest of the system.
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