# Homework Help: Weighing yourself in the elevator

1. Jul 5, 2009

### test2morrow

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

W=mg

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. Jul 5, 2009

### LowlyPion

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.