Force at point A and E (Static Equilibrium)

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Discussion Overview

The discussion revolves around a static equilibrium problem involving a man using a stepladder to fix a light bulb. Participants are tasked with finding the forces at points A and E of the ladder, given specific dimensions and conditions, including the weight of the man and the assumption of a frictionless floor.

Discussion Character

  • Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant describes the setup, including the dimensions of the ladder and the weight of the man, and asks for the forces at points A and E.
  • Another participant confirms the ladder is an A-frame and asks for the original calculations attempted by the first participant.
  • The first participant provides multiple force calculations for point A, yielding different results: 1220.38 N and 129.6 N, but expresses uncertainty about which is correct.
  • A subsequent post suggests drawing a free body diagram and finding angles, providing a formula for calculating the force at point A but questions the reasoning behind the calculations.
  • Further clarification is sought regarding the definitions of forces Fna and Fb, and the relevance of angles in the calculations, with a suggestion that calculating angles may not be necessary for accuracy.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct force values at points A and E, as multiple calculations yield different results. There is ongoing uncertainty regarding the methodology and reasoning behind the calculations.

Contextual Notes

Participants note potential issues with the assumptions made in the calculations, such as the necessity of angles and the treatment of forces at different points, which remain unresolved.

abcnat
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a man is trying to fix the light bulb at the top of his house ceiling.to reach the bulb,he is using a stepladder that is in equilibrium state.sides AC and CE are each 9.0 m long and hinged at C.Bar BD is attached with a rod that is 3.0 m long,halfway up.The man who is climbing 5.0 m along the ladder (AC) is 67 kg in weight.Assume that the floor is frictionless and the mass of the ladder is negligible.
Find the forces at points A and E.
 
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Welcome to PF;
Good question - I take it this is an A-frame ladder?
What have you tried so far?
 
yes with bar in the middle. I get 1220.38 N at point A and 928.58 N at point E.I also tried other calculation which i get 129.6 N at point A
 
That's neet - so which one is right?
I cannot tell unless you show me your working + your reasoning.
 
first draw free body diagram and find angle and stuff so
at point A
9(Fna sin 19.47)=4(mg cos 70.53) + 4.5(Fb cos 19.47)
9(Fna sin 19.47)=875.4 N + 2785.74 N
Fna=1220.38 N

but I'm not sure.the other calculation is pretty much the same but with different angle and get 129.6 N
so what did you get at point A?
overall i did 3 calculations all with different answers.please help me
 
Is Fna is the magnitude of the force at point A, normal to side AC
Is Fb the total force at point B?
What happened to the force at point C?
Which angle is 19.47deg?

... I cannot see your reasoning.

Note: you don't need to calculate any angles to do this problem - and your end result will be more accurate if you don't.

eg. let's call the angle ∠ACE is β, then cos(β)=1/3, sin(β)=(√2)/3
Each time you need a cosine of that angle, just write in 1/3.
 
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