Physics Question involving a person pulling himself up

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Homework Help Overview

The discussion revolves around a physics problem involving a person pulling themselves up using a rope attached to a spring scale and a pulley system. The scenario includes a swing/platform with specified weights and a tension reading from the scale, prompting questions about the direction of motion and forces involved.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the implications of the tension reading on the motion of the swing and the person. Questions arise about whether the person is going up or down, the role of the pulley, and the concept of mechanical advantage. Some participants suggest using free body diagrams to clarify the forces at play.

Discussion Status

The discussion is ongoing, with various interpretations being explored. Some participants have attempted calculations and drawn conclusions about the motion, while others seek clarification on the underlying principles and assumptions. There is no explicit consensus on the final outcome, but productive dialogue is evident.

Contextual Notes

Participants are working within the constraints of the problem as posed, including specific weights and the tension reading from the scale. The complexity of the system and the mechanics involved are acknowledged, with some participants questioning the feasibility of the proposed scenarios.

CoolGod
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A person is sitting on a swing/seat/platform and pulling himself up with a rope. Don't worry about the swing part. One end of the rope is attached to 2 other metal wires connected to the seat. The other end of the rope is attached to a spring scale and is being pulled by the person. The rope goes above and passes through a pulley. Like in this diagram. http://imageshack.us/a/img845/3343/phydia2.png
the swing weighs 160n, the person weighs 320n and the scale reads 250n.Is the swing/seat/platform going up or down? What is the force exerted by the person on the seat. What is the acceleration of the system.
Since scale reads 250n that should be tension in the rope. he must be exerting 250n. Thus 320+160 >250 thus he is going down.
The hard part of this question is that when the person pulls the rope/scale does the rope or scale pull him back up? Because if it does then technically he'd be going up. In this question can i replace his pull with a 250n block of mass? If he is going up, how is it possible for someone to exert 250n and move 480n up without mechanical advantage.
 
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Since scale reads 250n that should be tension in the rope. he must be exerting 250n. Thus 320+160 >250 thus he is going down.

Didn't I just read that the rope goes over a pulley. the rope is attached to the platfrom and the man is pulling on the other end.

Because if it does then technically he'd be going up. In this question can i replace his pull with a 250n block of mass

That would be a completely separate problem.

Best to draw one or 2 FBD ( free body diagram ), perhaps one of the man and one of the platfrom.
 
Hmm 256bits i don't understand where you are confused. fundamentally is he going up or down?
 
CoolGod said:
Hmm 256bits i don't understand where you are confused. fundamentally is he going up or down?

That's for you to figure out. Please show us your FBD(s).
 
i solved for the answer and he is going up. Since he pulls 2 m for every m he goes up, and work is same then it is similar to mechanical advantage of 2. Thus ((2*250)-480)/(480/9.81)=0.40875 m/s^2. so chair is accelerating at 0.40875m/s^2 and the force acting on it is fg 160n down fpc (missing force)down and tension 250n up so we get (250-160)-(0.40875*(160/9.81)) for fpc or 83.3333 N down.
 
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Looks OK to me .
 

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