Forces and Fnet

1. May 23, 2010

cheerspens

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

2. Relevant equations
FNET=ma

3. The attempt at a solution
I came up with the equation FEB-FGB=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?

2. May 23, 2010

Staff: Mentor

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

3. May 23, 2010

cheerspens

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

4. May 23, 2010

Staff: Mentor

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.