Analyzing Forces in a Platform and Pulley System

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Homework Help Overview

The discussion revolves around a physics problem involving a platform and pulley system, where a girl is attempting to accelerate upwards by pulling on a rope. The participants are exploring the forces acting on the system, including tension in the rope and normal forces between the girl and the platform.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply Newton's second law with the equation T - F = ma but expresses uncertainty about the problem. Some participants question whether the platform will move and discuss the implications of forces acting on the system.

Discussion Status

Participants are actively engaging with the problem, asking clarifying questions and exploring different interpretations of the forces involved. There is an exchange of ideas regarding the conditions necessary for the platform to accelerate upwards, and some guidance has been offered regarding the nature of the forces at play.

Contextual Notes

There is a mention of an uploaded image of the exercise, which may contain additional details relevant to the problem. Participants are also navigating assumptions about the movement of the platform and the forces exerted by the girl and the pulley system.

Paola Cavazos
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A girl stands on a platform and pulley system. The masses of the platform, girl and pulley are M, m and u respectively. The rope is mass-less. Let the girl pull up on the rope so that she accelerates a upwards. What is the tension of the rope? What is the normal force between the person and the platform? WHat is the tension connecting the pulley and the platform? I think that I should start from T - F = ma, but I really am kind of lost. I hope someone can help me find the accurate solution.

I uploaded an image of the exercise. Please help :)
 

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Paola Cavazos said:
I think that I should start from T - F = ma
You should explain your thinking when asking for help. How did you get this equation? What is it saying?
 
I have a small question Nathanael, I'm a bit confused with the problem too. Will the platform even move?? I'm sorry if this is a stupid question!
 
Suraj M said:
I have a small question Nathanael, I'm a bit confused with the problem too. Will the platform even move?? I'm sorry if this is a stupid question!
It's not a stupid question. I can see how one would think the platform may not move, because the harder you pull up on the rope, the harder your feet push down on the platform. But the upwards force on the platform from pulling is greater than the increased force downward from pushing with your feet.
For the platform to move upwards (or more specifically, for it to accelerate upwards) there has to a net upwards force acting on the system. If the other end of the rope was attached to the platform, and the person was pulling up on it, then clearly it could not move upwards. But since the end of the rope is attached to the ceiling, an upwards external force acts on the platform (and person) allowing upwards acceleration.
P.S.
I like your avatar.
 
I'm sorry but i still don't get how the upward force would be more than the downward. Could you explain?
 
Suraj M said:
I'm sorry but i still don't get how the upward force would be more than the downward. Could you explain?
I purposely left the specifics of that detail out so as not to ruin it for the OP :) I will explain it to you in a private message.
 

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