Barbara's Mass: How a Scale Reads in Different Situations

[cheerspens]

Homework Statement

Barbara has a mass of 60.0 kg. What would a metric bathroom scale (a scale that uses Newtons) read if she steps on it in the following situations:

On the Earth in an elevator experiencing an acceleration of 3.0 m/s² while speeding up and moving upward.

Homework Equations

F_NET=ma

The Attempt at a Solution

I came up with the equation F_EB-F_GB=ma
The mass would equal 60.0 kg and the acceleration 3.0 m/s² but how do I know what the scale would say?

 

[Doc Al]

but how do I know what the scale would say?

The scale reads the force it exerts against Barbara--what you call F_EB.

 

[cheerspens]

Then the scale would read 768N. So Fg is always the same but is not what is always read by the scale?

 

[Doc Al]

So Fg is always the same but is not what is always read by the scale?

Right. Fg is the force of gravity. The scale doesn't know anything about gravity, all it knows is the force pushing against it, which can change depending upon the acceleration. When the acceleration is zero, the scale reading equals Fg.