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Homework Help: Elevator - Tension

  1. Feb 13, 2010 #1
    1. The problem statement, all variables and given/known data

    A 563 N physics student stands on a bathroom scale in an 823 kg (including the student) elevator that is supported by a cable. At some time during her elevator ride, the scale reads 400 N.

    Find the acceleration of the elevator.

    Found this to be 2.84 m/s2 in the down direction.

    What is the tension in the cable?

    This is what i am having trouble with.


    2. Relevant equations

    F=ma

    3. The attempt at a solution

    I thought the tension in the elevator would just be the mass of the elevator and student 823 kg times by the acceleration of the elevator?

    T = 823(2.84) = 2337 N

    This is wrong though.

    Help please :)

    Thank you
     
  2. jcsd
  3. Feb 13, 2010 #2
    AHHH! nevermind i didnt take gravity into consideration.
     
  4. Feb 13, 2010 #3

    PhanthomJay

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    Science Advisor
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    Gold Member

    You determined the acceleration correctly; in so doing, you must have condsidered both the student's weight and the normal force of the scale on the student in determining the net force acting on the student. Now do the same looking at the elevator; the net force is comprised of more than one force.
     
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