Simple Static Equilibrium question

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Discussion Overview

The discussion revolves around a static equilibrium problem involving two workers carrying a beam. The participants explore the mechanics of forces acting on the beam, specifically focusing on the distances at which the workers hold the beam and the calculations involved in determining these distances. The scope includes mathematical reasoning and conceptual clarification related to moments and forces.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One worker carries 0.4 of the beam's weight while holding it at the edge, prompting the question of where the second worker must hold the beam.
  • Some participants suggest using the sum of moments about the center of gravity to solve for the unknown distance.
  • There is a discussion about the necessity of a clear diagram to visualize the problem and the forces involved.
  • One participant expresses confusion over their calculations and the relationship between the distances involved.
  • Another participant points out that the diagram provided by the original poster is unclear and lacks proper markings for the distances.
  • Participants discuss the importance of carefully reading the problem statement to avoid misinterpretations.

Areas of Agreement / Disagreement

Participants generally agree on the approach of using moments to solve the problem, but there is uncertainty regarding the calculations and the clarity of the diagram. The discussion remains unresolved as participants work through the problem collaboratively.

Contextual Notes

Some participants mention difficulties in visualizing the problem without a diagram, and there are unresolved mathematical steps regarding the calculation of moments and distances.

Femme_physics
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Homework Statement



Two workers carry a beam at the length of 3 meters. One worker holds the beam at the edge and carries 0.4 of the beam's weight. At what distance (x) from the other edge holds the second worker?

Homework Equations



None.

The Attempt at a Solution



The solution is x = 0.5 [m]

I just don't know the way... can anyone help me understand this?
 
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Hi Dory! :smile:
Dory said:
Two workers carry a beam at the length of 3 meters. One worker holds the beam at the edge and carries 0.4 of the beam's weight. At what distance (x) from the other edge holds the second worker?

Hint: there are three forces on the beam …

the weight operating through the centre of mass, and the two forces from the workers. :wink:
 
tiny-tim said:
Hi Dory! :smile:


Hint: there are three forces on the beam …

the weight operating through the centre of mass, and the two forces from the workers. :wink:

Hi!

There are 3 forces, yes, mg, and the 2 workers. I've tried calculating the sum of all moments on all 3 points but something isn't right in my answers, and I'm not even sure if I'm using the right equations. I'm not used to these questions coming without diagrams...
 
Take moments about anywhere, and it should work …

show us what you get. :smile:
 
Now is your chance to do a diagram of your own and which demonstarates YOUR understanding of this problem.
 
Sum of all moments on G (center of gravity) = 0.4mg x 1.5 -0.6mg x (unknown length)

If I do that the result is 1...? That can't be the answer...it says the answer is 0.5 [m]...

As for the free body diagram...there... arg...still can't see how...darn it, I solved muuuuuuuuuch harder problems than this...that's annoying I can't figure it out!


http://img405.imageshack.us/img405/5662/thereh.jpg
 
Last edited by a moderator:
Dory: Nice work. Your result is correct, so far. Now, the question asks you for the distance, x, measured from the left-hand edge. Can you think of how to compute it?
 
Well, there are 2 distances here really. 3 meter (distance from worker to worker) and 1.5 meter, distance from worker to center of gravity. Do you see any more distances?
 
You have got the 0.6 at 3m from the 0.4, but it should be x from there. This is a moments question, but first, get your figure right.
 
  • #10
Hi Dory! :smile:

(just got up :zzz: …)
Dory said:
… At what distance (x) from the other edge holds the second worker?
Dory said:
Sum of all moments on G (center of gravity) = 0.4mg x 1.5 -0.6mg x (unknown length)

If I do that the result is 1...? That can't be the answer...it says the answer is 0.5 [m]...

D'oh! :rolleyes:

That is right! You got 1 from the centre, which is 0.5 from the edge! :smile:

Always read the question carefully!

btw, sorry but your diagram is really bad …

you haven't marked "x" on it at all, and you've put both the forces at the ends.

A clear diagram is essential for doing these questions (although you don't get any marks for the diagram in an exam, you certainly lose marks if you make mistakes because your diagram is bad, and you can also lose time :redface:)​
 
  • #11
Oh, so I made a mistake in the diagram, they're holding it some distance AWAY from the edge... ah...got it, thanks :D

Thanks for leading me up to it!
 

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