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Find the direction of acceleration

  1. Sep 30, 2011 #1
    1. The problem statement, all variables and given/known data

    A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.66 of the person's regular weight. Calculate the acceleration of the elevator, and find the direction of acceleration.

    2. Relevant equations

    So I know you have to use sumF = MA to solve this problem.

    3. The attempt at a solution

    I drew a freebody diagram.
    | Fn
    | .66mg

    And I got the formula N - .66mg = .66ma. This where I get stuck. I don't know what to do next.

    As for the second part of the question, I know that the elevator is moving downward because of the decrease in mass.
  2. jcsd
  3. Sep 30, 2011 #2
    Re: Elevators

    The normal force is 0.66mg and the person's weight is mg.
  4. Sep 30, 2011 #3
    Re: Elevators

    So I took that into account and got

    .66mg - mg = .66ma
    -.44 = .66ma
    -.66 = ma.

    Now I don't know what to do with the m. :\
  5. Sep 30, 2011 #4
    Re: Elevators

    The mass is considered to still be m on the right side of the equation. Also, 0.66mg - mg = -0.34mg.
  6. Sep 30, 2011 #5
    Re: Elevators

    Thank you. I feel very stupid right now for not noticing that arithmetical mistake.
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