Static Equilibrium - trick question?

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Homework Help Overview

The problem involves a man standing on a board supported by two cables with specified tensions. The objective is to determine the man's weight based on the forces and torques acting on the system.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to set up a torque equation but expresses uncertainty about the man's position and weight. They also consider summing forces along the y-axis but question if they are overcomplicating the situation.

Discussion Status

Some participants suggest that the problem may be simpler than it appears, indicating that the original poster might be overthinking the solution. There is acknowledgment of the context of previous, more complex problems leading to confusion.

Contextual Notes

No angles for the cables are provided, leading to assumptions about their verticality. The problem is presented after more challenging questions, which may contribute to the original poster's hesitation.

prettydumbguy
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Homework Statement



A man stands on a board of negligible mass with a length of 10m is supported by 2 cables, one on the left on one on the right, with a tension of 300N and 200N respectively. How much does the man weigh in Newtons?

Homework Equations


F=ma
Torque= F*lever arm

The Attempt at a Solution


I'm tempted to just 500, but that's far to simple. I thought of setting up a torque equation, but I don't know how I would when I don't know his mass or where he stands. So, if I assume he's standing x meters from the left: 300(x)-200(10-x) + man(mans location) = 0.
So I set one of the cables as the axis of rotation: the left cable, giving me man(x)=200(10).
Multiply out to get man(x) = 2000.
Now I have two variables I can't get rid of.

But I still really want to just sum all the forces along the y-axis and set it equal to zero: 300 + 200 -man = 0, so I still get 500.
Am I just overthinking the hell out of this?
 
Last edited:
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Assuming the cables are vertical, yes, you're overthinking it. It is as easy as it seems.
 
haruspex said:
Assuming the cables are vertical, yes, you're overthinking it. It is as easy as it seems.
No angles were given, so I assume that they are vertical. The question comes after two much more in depth SE problems, hence my confusion. Thanks!
 
prettydumbguy said:
No angles were given, so I assume that they are vertical. The question comes after two much more in depth SE problems, hence my confusion. Thanks!
Sounds like a classic way to catch people out, follow some tough questions by an easy one with redundant information.
There's an old geometry problem where you ask someone to cut an L shape, consisting of three squares, into four identical pieces. When they've solved it, you say ok, try this harder one: cut a square into five identical pieces.
 

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