Calculating Elevator Acceleration: Solve for F=ma

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Homework Help Overview

The problem involves calculating the acceleration of an elevator based on the readings of a bathroom scale when the elevator begins to move. The subject area is dynamics, specifically focusing on forces and acceleration as described by Newton's second law (F=ma).

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the setup of the problem, questioning the forces acting on the person during the elevator's acceleration. There are attempts to clarify the equations used and the reasoning behind them, particularly concerning the force of gravity and tension.

Discussion Status

The discussion is ongoing, with participants offering insights into the forces involved and questioning each other's reasoning. Some guidance has been provided regarding the setup of equations, but there is no explicit consensus on the correct approach yet.

Contextual Notes

Participants note that the only numerical information provided is the scale reading of 1.05 times the person's regular weight when the elevator starts accelerating. There is also mention of the potential for variables to cancel out in equations, which has led to confusion.

Jeff Nilsson
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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 1.05 times the persons regular weight. Calculate the magnitude and direction of the acceleration of the elevator.

Homework Equations


F=ma

The Attempt at a Solution


Fg = 9.8m
ΣF = 9.8(1.05m + m)
0 = 1.05m + m
-m = 1.05m
-1 = 1.05

I know that's not true but I don't really know how to set up the problem
 
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Jeff Nilsson said:
ΣF = 9.8(1.05m + m)
Please explain your reasoning behind this equation.
What forces act on the person during the acceleration?
What acceleration results?
 
haruspex said:
Please explain your reasoning behind this equation.
What forces act on the person during the acceleration?
What acceleration results?

Actually the equation would be ΣF=9.8m-9.8(1.05m+m) according to my logic
but ΣF in this case is the difference between the force of gravity and the force of tension
the 9.8m part is to find the force of gravity on the person in the motionless elevator and the 9.8(1.05m+m) part is to find the force acting on the person when the elevator starts accelerating upward
to find ΣF you subtract the force of gravity from the fore of tension since it is larger
my physics teacher said that sometimes if you set up equations without numbers the variables will cancel out so I tried that and nothing cancels
The only number the problem gives me is 1.05 times the original weight when the elevator starts accelerating
and since the person is inside the elevator it's a system and the forces acting on the elevator vary directly with the forces acting on the person
 
Jeff Nilsson said:
the 9.8(1.05m+m) part is to find the force acting on the person when the elevator starts accelerating upward
Maybe I misunderstand your notation, but that appears to reduce to 9.8(2.05)m. Is that what you meant?

Jeff Nilsson said:
nothing cancels
It will. When you have corrected your "9.8(1.05m+m)" and written it in simplest form, equate it to "ma", as in ΣF=ma.
 

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