Bending stress–section modulus relation in beams For a prismatic beam subject to bending moment M, use the flexure formula. Choose how bending stress varies with section modulus.
Mechanical Engineering
Strength of Materials
Difficulty: Easy
Choose an option
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ADirectly proportional to section modulus
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BInversely proportional to section modulus
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CEqual to section modulus
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DIndependent of section modulus
Answer
Correct Answer: Inversely proportional to section modulus
Explanation
Concept/FormulaFlexure formula: σ = M y / I. Section modulus Z = I / y. Therefore, σ = M / Z.
ImplicationFor a given bending moment M, increasing Z (by choosing a stiffer cross-section) reduces the bending stress linearly.
Final AnswerInversely proportional to section modulus.