Solving Dynamics Homework: Man on Elevator, 60 kg Mass

[jey1234]

Homework Statement

I'm confused w/ a dynamic question our teacher showed us today. we just started dynamics and I'm in grade 11. I made a horrible diagram on ms paint but I believe it will suffice :) A man is standing in an elevator on a scale. The elevator is moving up at 5m/s^2 and then there is the obvious gravitational pull. What will be the reading on the scale, in Newtons (so force?), if the man's mass is 60 kg?

Homework Equations

She told us to use a= F_R/m

The Attempt at a Solution

The thing is she solved it for us and I can't seem to understand her steps. She says to find the individual Forces of both accelerations. So F=ma

F₁= 60kg * 5 m/s^2 [UP]
F₂= 60kg * 9.81 m/s^2 [DOWN]

This is the part that confuses me: F_R= F₂-F₁
We've never done subtraction of vectors before, and she explained that we change the direction of the second vector and just add it.

Therefore, F₁= 300N [UP] , F₂= 588.6N [DOWN]
which becomes: 588.6N [DOWN] + 300N [DOWN] = 888.6N [DOWN] <--- HER FINAL ANSWER

My first question is since the whole system is affected by the two accelerations doesn't "cancel" out? In other words, although he is moving up at 5m/s^2 and down at 9.81m/s^2, the scale is also experiencing those movements, therefore it will almost be like "at rest". If I was to do it, I would ignore them, and simply calculate his weight: 60kg * 9.81 m/s^2 [DOWN] = 588.6N [DOWN]. If not, I would add the two accelerations and get: 9.81m/s^2 [DOWN] + 5m/s^2 [UP] = 4.81m/s^2 [DOWN] (basically subtracting them and keeping the larger ones direction). After, I'd multiply that by mass and get: 60kg * 4.81m/s^2 [DOWN] = 288.6N [DOWN].

Are one of my methods and/or my teacher's right? If not, please explain why. Thanks!

Homework Statement

Homework Equations

The Attempt at a Solution

 

[jey1234]

+bump (sorry)