The problem involves a man pulling on a rope connected to a pulley, with the goal of determining the magnitude of the force required for him to rise with a constant velocity or with a specified upward acceleration. The combined weight of the man and chair is given as 95 kilograms.
The discussion is actively exploring the forces involved, with participants revising their understanding of the Free Body Diagram based on clarifications about the pulley and the setup. There is an acknowledgment of multiple tensions acting on the system, and participants are questioning the signs of the forces involved.
Participants are working under the assumption that the pulley is frictionless and are clarifying the setup of the rope and its connection to the chair. There is a focus on understanding the net forces and their directions without reaching a final conclusion.
Is the man pulling himself and his chair up and does the rope loop around a pulley attached to the ceiling? (A diagram will help.)passphysicsC said:A man is strapped to a chair which is connected to a pulley (combined weight of chair and person = 95 kilograms). With what magnitude must the man pull on the rope if he is to rise
I'll rephrase my question. Draw an imaginary box around the 'man + chair' contraption. How many ropes pass through the boundary of that box?Doc Al said:Hint: How many times does the rope pull up on the 'man + chair'?
Good! There would be two separate tensions acting. (Not necessarily different though.) One end of the rope pulls up on his hands; the other pulls up on his chair. They both count towards the net force on the 'man + chair'.passphysicsC said:then two ropes, one rope connected to the chair, and one rope which the man uses to pull himself and the chair up...would there be two different tensions then?
I find that very confusing.passphysicsC said:alright, so then the Net Tension = ((mass x acceleration) + weight) + (mass x acceleration)?
What direction do these force have? (Do they all have the same sign?)passphysicsC said:Σf = (t + w) + (t)
OK. The rope pulls up on the chair, thus is a positive force.passphysicsC said:well the first tension is positive since it is holding the chair and man up.
The weight acts down, so is negative.the weight (w) is negative since it the force working against the tension.
All we care about are forces on the man/chair. The rope pulls up on the man and up on the chair. Both tension forces are positive.I believe the last tension would be negative since it is caused by the man pulling on the rope to pull himself and the chair up.