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

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To determine the force required for a man weighing 780 N to lift himself using movable pulleys, the tension in the rope must equal half of his weight due to the mechanics of the pulley system. The initial calculation suggested that pulling with a force of 390 N would suffice, but this was incorrect. The correct approach indicates that the total tension must equal the man's weight, leading to the conclusion that he needs to exert a force of 780 N to lift himself steadily. The absence of an acceleration value in the problem complicates the calculations, but ultimately, the solution was found. Understanding the dynamics of tension in pulley systems is crucial for solving such problems effectively.
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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.

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____________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 alot.
 
nevermind i figured it out, thanks
 
Thread 'Correct statement about size of wire to produce larger extension'

Thread 'Correct statement about size of wire to produce larger extension'

The answer is (B) but I don't really understand why. Based on formula of Young Modulus: $$x=\frac{FL}{AE}$$ The second wire made of the same material so it means they have same Young Modulus. Larger extension means larger value of ##x## so to get larger value of ##x## we can increase ##F## and ##L## and decrease ##A## I am not sure whether there is change in ##F## for first and second wire so I will just assume ##F## does not change. It leaves (B) and (C) as possible options so why is (C)...
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