Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Shear stress is a type of normal stress that acts in a direction perpendicular to the cut surface of any object.
Reason (R) : Shear stress is the one that acts parallel or tangential to the surface.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Stress types:
• Normal stress → perpendicular to surface
• Shear stress → parallel to surface Examples:
• Tension/compression → normal stress
• Cutting action → shear stress

Answer 1

The Correct Option is D

Concept: Stress is the internal resisting force developed within a material per unit area. Two important types are:
• Normal stress → acts perpendicular to the surface
• Shear stress → acts parallel or tangential to the surface

Step 1: Analyze Assertion (A).
The assertion states that shear stress acts perpendicular to the cut surface. This is incorrect because stress acting perpendicular to the surface is called normal stress, not shear stress. Hence, Assertion (A) is incorrect.

Step 2: Analyze Reason (R).
Shear stress acts parallel or tangential to the surface of the material. \[ \tau = \frac{F}{A} \] where:
• \(F\) = tangential force
• \(A\) = area resisting shear Hence, Reason (R) is correct.

Step 3: Choose the correct option.
Assertion (A) is false, but Reason (R) is true. Therefore, the correct answer is: \[ {\text{(D) (A) is not correct but (R) is correct}} \]