Find the direction of acceleration

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Homework Help Overview

The problem involves analyzing the forces acting on a person standing on a bathroom scale in a moving elevator. The scenario describes a situation where the scale reads a reduced weight, prompting the calculation of the elevator's acceleration and its direction.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of Newton's second law and the implications of the normal force being less than the person's weight. There are attempts to set up equations based on free-body diagrams and to manipulate these equations to isolate variables.

Discussion Status

Participants are engaged in exploring the relationships between forces and acceleration. Some have provided insights into the calculations, while others express uncertainty about handling variables and arithmetic errors. There is a recognition of mistakes made in earlier calculations, which has led to further clarification and discussion.

Contextual Notes

Participants are navigating the implications of the normal force being less than the gravitational force, which raises questions about the direction of acceleration and the assumptions made regarding mass and forces in the equations.

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Homework Statement



A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.66 of the person's regular weight. Calculate the acceleration of the elevator, and find the direction of acceleration.

Homework Equations



So I know you have to use sumF = MA to solve this problem.

The Attempt at a Solution



I drew a freebody diagram.
^
|
| Fn
.
|
| .66mg
V

And I got the formula N - .66mg = .66ma. This where I get stuck. I don't know what to do next.

As for the second part of the question, I know that the elevator is moving downward because of the decrease in mass.
 
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The normal force is 0.66mg and the person's weight is mg.
 


So I took that into account and got

.66mg - mg = .66ma
-.44 = .66ma
-.66 = ma.

Now I don't know what to do with the m. :\
 


The mass is considered to still be m on the right side of the equation. Also, 0.66mg - mg = -0.34mg.
 


Thank you. I feel very stupid right now for not noticing that arithmetical mistake.
 

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