1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Weighing yourself in the elevator

  1. Jul 5, 2009 #1
    Need help:Weighing yourself in the elevator-acceleration problem

    1. The problem statement, all variables and given/known data

    If you stand on a spring scale in your bathroom at home, it reads 600N, which means your mass is 60kg. If instead, you stand on the scale while accelerating at 2 m/s^2 upward in an elevator, what would the scale read?

    a. 120N
    b. 480N
    c. 600N
    d. 720N

    2. Relevant equations


    3. The attempt at a solution

    So I asked my professor this question and he came up with some complicated answer that I didn't really understand. My own logic was that W=mg, W=60kg * (2m/s^2+9.8m/s^2), W=720N which is the correct answer. However, this is not the same steps the professor used which was something like F=N-W=ma and he did some subtraction work and somehow got 720N.

    So can somebody explain to me the correct way to solve this problem?
    Last edited: Jul 5, 2009
  2. jcsd
  3. Jul 5, 2009 #2


    User Avatar
    Homework Helper

    Re: Need help:Weighing yourself in the elevator-acceleration problem

    That works too of course.

    The 60 kg student is accelerating upward at 2 m/s2. The Normal force of the student less the gravitational weight must yield an m*a of the same acceleration as the floor.
    N is what the spring will register and rearranging that normal force = m*a + W = m*(g + a)

    Your way works fine as well.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook