What is the required force to lift oneself using movable pulleys?

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Homework Help Overview

The problem involves determining the force required for a man to lift himself using movable pulleys, with a total weight of 780 N for the man and platform. The pulley system is modeled as frictionless.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between tension and weight, with one participant attempting to apply equations of equilibrium. Questions arise regarding the assumptions made about acceleration and the implications of not having that information.

Discussion Status

Some participants have offered different interpretations of the problem, with one suggesting that the tension equals the weight directly, while another has expressed confusion over previous attempts. The discussion reflects a mix of reasoning and exploration of concepts without a clear consensus.

Contextual Notes

There is a noted lack of information regarding acceleration, which some participants believe is critical to solving the problem. Additionally, there are indications of previous attempts being incorrect, leading to further questioning of the setup.

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1. Homework Statement

In the figure below, the man and the platform together weigh 780 N. The pulley can be modeled as frictionless. Determine how hard the man has to pull on the rope to lift himself steadily upward above the ground.

p4-33.gif


____________N



2. Homework Equations

I didn't use any until it said i was wrong but here is what it would be:

mg = T(1) + T(2)
T(1) = T(2)



3. The Attempt at a Solution

mg = 780 N = 2*T(1)

780 N / 2 = T(1)

390 N = T(1)

I first entered 390 and it was wrong, then I tried 391 to steadily move it upward. Both were wrong. Any help?
 

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cant anyone help
 
I believe the answer is simply T = 780 N.

T - mg = m(0)
T = mg = 780 N

They didn't give you any value for the acceleration which if they did would've changed a lot.
 
nevermind i figured it out, thanks
 

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