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

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Homework Help Overview

The problem involves understanding how a scale measures weight in different acceleration scenarios, specifically when a person with a known mass is in an elevator that is accelerating upward. The subject area pertains to forces and Newton's laws of motion.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between the forces acting on the scale and the readings it provides, questioning how acceleration affects the scale's measurement compared to the force of gravity.

Discussion Status

Some participants have clarified the distinction between the gravitational force and the force exerted by the scale, noting that the scale reading can vary with acceleration. There is an ongoing exploration of how these forces interact, but no consensus has been reached on the specific reading in the given scenario.

Contextual Notes

Participants are considering the effects of acceleration on scale readings, with a focus on the implications of different forces acting in an elevator context. The original poster's question reflects a common confusion regarding the relationship between mass, gravitational force, and scale readings under varying conditions.

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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


FNET=ma


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?
 
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cheerspens said:
but how do I know what the scale would say?
The scale reads the force it exerts against Barbara--what you call FEB.
 
Then the scale would read 768N. So Fg is always the same but is not what is always read by the scale?
 
cheerspens said:
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.
 

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