Mechanics of Materials segment choosing

Click For Summary

Discussion Overview

The discussion revolves around the mechanics of materials, specifically focusing on the selection of segments for analysis in shear force calculations. Participants explore the implications of choosing different segments (AC vs. CB) and how this affects the calculated shear forces.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the concentrated force is 40 kN and has calculated B(y) as -10 kN, with A(y) being 50 kN, but questions how to choose the segment for analysis.
  • Another participant requests clarification on how to derive a shear force of 50 kN when analyzing segment AC.
  • A participant asserts that since A(y) is 50 kN, C(y) must also be 50 kN, but acknowledges that this value could vary depending on the chosen region.
  • Another participant points out that in the force balance on segment AC, the downward shear force on the left side of cross section A was omitted.
  • A participant confirms understanding that the external forces of 50 kN and 40 kN necessitate an internal shear force of 10 kN to maintain equilibrium.

Areas of Agreement / Disagreement

Participants express differing views on the implications of segment choice for shear force calculations, indicating that there is no consensus on the best approach to selecting segments for analysis.

Contextual Notes

Participants highlight the importance of understanding the effects of segment choice on calculated shear forces, suggesting that the analysis may depend on specific assumptions and the chosen reference points.

mastermechanic
Messages
107
Reaction score
15

Homework Statement


0BYjDB.png


Homework Equations


Torque = F. d
Distributed Force -> Concentrated Force = w.d

The Attempt at a Solution


Concentrated force is equal to 40kN and I have found the B(y) as -10kN by taking moment with respect to the A point. And from the equilibrium A(y) is 50 kN.

Everything is good so far. But my problem is about to choosing the segment which I will analyze. The book shows the CB and finds the shear force 10 kN. But if I choose AC part, it is 50 kN. How do we decide to choose which segment will be analyzed? I mean what is the key point? If it is arbitrary, what did I miss to take into account and why it is not taken into account while choosing the part CB?

Thanks!
 
Physics news on Phys.org
mastermechanic said:

Homework Statement


View attachment 210010

Homework Equations


Torque = F. d
Distributed Force -> Concentrated Force = w.d

The Attempt at a Solution


Concentrated force is equal to 40kN and I have found the B(y) as -10kN by taking moment with respect to the A point. And from the equilibrium A(y) is 50 kN.

Everything is good so far. But my problem is about to choosing the segment which I will analyze. The book shows the CB and finds the shear force 10 kN. But if I choose AC part, it is 50 kN. How do we decide to choose which segment will be analyzed? I mean what is the key point? If it is arbitrary, what did I miss to take into account and why it is not taken into account while choosing the part CB?

Thanks!
Show us how you get a shear force of 50kN choosing AC please.
 
Chestermiller said:
Show us how you get a shear force of 50kN choosing AC please.
Q76X4G.png
A(y) is 50 kN so C(y) must be 50 kN. It is weird, it can be any value even 0 depending on the region. So, I should know respect to what we choose the region.
 
mastermechanic said:
View attachment 210011 A(y) is 50 kN so C(y) must be 50 kN. It is weird, it can be any value even 0 depending on the region. So, I should know respect to what we choose the region.
In your force balance on AC, you omitted the downward shear force on the left side of cross section A.
 
Chestermiller said:
In your force balance on AC, you omitted the downward shear force on the left side of cross section A.
50 kN and 40 kN are external forces. So you're saying there must be shear force of 10 kN internal shear force to compansate it, right? I think I understand it thank you!
 
  • Like
Likes   Reactions: Chestermiller

Similar threads

  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
5
Views
4K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 22 ·
Replies
22
Views
3K
  • · Replies 4 ·
Replies
4
Views
5K
  • · Replies 46 ·
2
Replies
46
Views
15K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 9 ·
Replies
9
Views
4K