Net Force of 60 kg Person in Elevator: Up/Down

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Homework Help Overview

The discussion revolves around calculating the net force acting on a 60 kg person in an elevator that is accelerating at 5 m/s², both when the elevator is moving upwards and downwards. The problem involves concepts from dynamics, specifically Newton's second law of motion.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculations for net force in both upward and downward scenarios, questioning whether the original poster's answers are correct. There is also a focus on distinguishing between net force and normal force, with some participants suggesting that the normal force must exceed gravitational force for the elevator's acceleration to be maintained.

Discussion Status

The discussion is ongoing, with participants seeking clarification on the definitions of net force and normal force. Some guidance has been provided regarding the relationship between these forces and the conditions necessary for the elevator's acceleration, but no consensus has been reached regarding the correctness of the original calculations.

Contextual Notes

Participants are navigating the implications of different forces acting on the person in the elevator, particularly in relation to the gravitational force and the elevator's acceleration. There is an emphasis on understanding the setup of the problem and the definitions involved.

barthayn
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Homework Statement



What is the net force of a 60 kg person, in Newtons, in an elevator accelerating at 5 m/s/s;
a) upwards?
b) downwards?

Homework Equations


F = ma


The Attempt at a Solution



a) F = 60 (5+9.8)
F = 60 * 14.8
F = 888 N [up]

b) F = 60 (-5+9.8)
F = 60 * 4.8
F = 288 N


Are my answers correct? If they are it is because you have to use vectors and do the change in acceleration to get the acceleration correct?
 
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Net force on the person or the normal force on the person by the elevator?
 
Apphysicist said:
Net force on the person or the normal force on the person by the elevator?

Net force on the person. The normal force would just be mass multiplied by the acceleration due to gravity correct?
 
barthayn said:
Net force on the person. The normal force would just be mass multiplied by the acceleration due to gravity correct?

Actually no. If you consider that the forces on the person are just the normal force of the elevator on the person and the gravitational force, in order to have a net acceleration of 5m/s2 of both the person and elevator, your normal force has to exceed the gravitational force.

At least that's how I read the problem. I see elevator problems and they usually ask for the normal force, since given a net acceleration and gravitational force, the normal force is what is unknown.
 
So is my answers for the net force of the person correct? Which are:

a) F = 60 (5+9.8)
F = 60 * 14.8
F = 888 N [up]

b) F = 60 (-5+9.8)
F = 60 * 4.8
F = 288 N [down]
 

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