Engineering Statics Question Regarding Finding Normal Force

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Discussion Overview

The discussion revolves around a problem in engineering statics involving the calculation of the normal force exerted by a wall on a beam in equilibrium. Participants analyze the forces acting on the beam and the moments about a specific point to derive the normal force value.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant begins by analyzing the pulley system, concluding that each cable carries a force of 100N and sets up an equation based on the moment about point B to find the normal force.
  • Another participant points out a potential issue with the normal force being perpendicular to the beam, noting that a component of this force would act parallel to the wall, which is frictionless.
  • Subsequent posts acknowledge the mistake and discuss the need to determine the angle for the component of the normal force acting perpendicular to the beam.
  • A participant presents a revised equation for the sum of moments about point B, leading to a new calculation for the normal force, suggesting it to be 300N.
  • Another participant agrees with the revised calculation but raises a question about the direction of the normal force acting on the wall.

Areas of Agreement / Disagreement

Participants acknowledge mistakes and refine their calculations, but there is no consensus on the final interpretation of the normal force's direction or its implications.

Contextual Notes

Participants discuss the geometry of the forces involved, including angles and components, but do not resolve the implications of these factors on the final answer.

Temp0
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Homework Statement


http://i.imgur.com/rwbXqW8.png


Homework Equations





The Attempt at a Solution


So I started off by analyzing the pulley, and determined that each cable carries 100N of force. After that, I drew the FBD of the beam, where there is a 100N force going downwards on the right end and the normal force perpendicular to the beam on the left end. I took the moment about point B, and since this is in equilibrium, the moment should be zero. Therefore I came up with the equation:

-100cos(30)(0.3) + Nwall (0.1) = 0
Where Nwall is the normal force provided by the contact with the wall.
I came up with the answer 259.8N, can anyone check my work please? Thank you in advance.
 
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Temp0 said:

Homework Statement


http://i.imgur.com/rwbXqW8.png


Homework Equations





The Attempt at a Solution


So I started off by analyzing the pulley, and determined that each cable carries 100N of force. After that, I drew the FBD of the beam, where there is a 100N force going downwards on the right end and the normal force perpendicular to the beam on the left end. I took the moment about point B, and since this is in equilibrium, the moment should be zero. Therefore I came up with the equation:

-100cos(30)(0.3) + Nwall (0.1) = 0
Where Nwall is the normal force provided by the contact with the wall.
I came up with the answer 259.8N, can anyone check my work please? Thank you in advance.
If the normal force at the left end was perpendicular to the beam, then there would be a component of that force acting parallel to the wall. But the wall is frictionless. So...?
 
Yeah I noticed my mistake, the beam will create a contact force that's perpendicular to the wall and I need to figure out the angle for the component perpendicular to the beam where I can then take the moment.
 
Temp0 said:
Yeah I noticed my mistake, the beam will create a contact force that's perpendicular to the wall and I need to figure out the angle for the component perpendicular to the beam where I can then take the moment.
Yes, that will work.
 
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So, for my final equation, I found that the normal force of the wall is 30 degrees from the perpendicular component to the beam, so I have:
The sum of moments about point B = Nwall cos30 (0.1) - 100cos30(0.3) = 0
Getting an Nwall of 300.
 
Temp0 said:
So, for my final equation, I found that the normal force of the wall is 30 degrees from the perpendicular component to the beam, so I have:
The sum of moments about point B = Nwall cos30 (0.1) - 100cos30(0.3) = 0
Getting an Nwall of 300 N .

Looks good!
I suppose you should indicate its sense...whether the force of the beam on the wall perpendicular to the wall is acting up and to the left or down and to the right... ?
 

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