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Reference frames

  1. Mar 15, 2013 #1
    someone please help me out with this question:

    You are in an elelvator that is able to travel up and down a mineshaft. a load is hung from the ceiling inside the elevator on a massless string. You find that the tension in the rope is 10% less than that of the weight force of the load. what can be said about the elevator?;

    1./ it's an inertial reference frame
    2./it's a non-inertial refernce frame
    3./it's moving up at a constant velocity
    4./moving down with a constant velocty
    5./must be accelerating

    I'm thinking 2./ and 5./ but definitely not sure. Could someone walk me through reference frames in this context and help me understand what is going on?
  2. jcsd
  3. Mar 15, 2013 #2


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    your answers are correct. You must have had some basis for choosing those - what was your reasoning? What is meant by an inertial frame?
  4. Mar 15, 2013 #3
    Well I figured that the elevator is a non inertial frame of reference as there must be some kind of acceleration. But if that's so I thought the newtonian mechanics would break down, and the only thing that could cause tension in the string to be different to the weight load would be a force applied on the rope in the elevator (e.g the load being pulled up or down relative to the elevator). So I thought that the motion of the elevator would have no effect on the string in the elevator
  5. Mar 15, 2013 #4


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    Do you understand that when the question mentions 'weight force load' it means what the force would have been had the elevator been stationary?
    When an elevator starts to go up, what do you notice about the forces on your legs?
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