Solid Mechanics(Stress Question)

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Discussion Overview

The discussion revolves around a solid mechanics problem related to stress calculations in a structural context. Participants are analyzing a homework question involving the relationship between forces and stresses in different shafts, with a focus on verifying calculations and comparing results to a provided textbook answer.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents an initial calculation for stress, equating stress in two different sections and arriving at a value of P = 18.4615 kips.
  • Another participant checks the math and recalculates P to be 18.5 kips, suggesting the initial equations were correct.
  • A different participant notes that their homework indicates the correct answer should be 28.2 kips, raising a question about the source of this discrepancy.
  • Further, it is argued that if P is 28.2 kips, the resulting stresses in the shafts would not be equal, indicating a significant difference in the calculated values.
  • One participant expresses agreement with the initial calculation and suggests that the textbook answer may be incorrect.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are multiple competing views regarding the correct value of P and the validity of the textbook answer. Some participants support the initial calculations, while others reference the textbook answer, leading to an unresolved discussion.

Contextual Notes

There are unresolved assumptions regarding the conditions of the problem and the definitions of stress being used. The calculations depend on specific interpretations of the problem setup, which may not be fully articulated.

zack7
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Homework Statement


In the picture below

Homework Equations


Stress=P/A

The Attempt at a Solution


I equated stress AB=-stress BC
p/pi=-(p-60 kips)/2.25pi

P=18.4615kips
This is not the right answer according to the book
 

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Does anybody know whether my answer is right or wrong?

Thank you
 
Well you have the correct equations...so let's check the math;;;
P/pi = (60-P)/2.25(pi)
2.25P = 60 -P
3.25P = 60
P = 18.5 K

Looks Good!
 
But for my homework, I got this question wrong and in the book the answer is 28.2kips
 
I don't know where that answer comes from...If P =28.2 K, then the force in the fat shaft would be woul be 31.8 K compression; and the tensile stress in the thin shaft would be 9 ksi, while the compressive stress in the fat one would be 4.5 ksi...far from equal in magnitude... off by a factor of 2..
 
zack7: Nice work. I currently agree with your answer in post 1, and with the answer by PhanthomJay[/color]. The answer in the book currently appears wrong.
 
Last edited:

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