Mechanical Properties Of Solids

To determine the correct answer, let's examine the assertion and reason statements separately in the context of physics:

Assertion (A): "The stretching of a spring is determined by the shear modulus of the material of the spring."

The assertion is correct. The behavior of springs, particularly the amount they stretch or compress, is influenced by the shear modulus (also known as modulus of rigidity) of the material. The shear modulus is a measure of a material's ability to withstand shear deformation. For helical coils, which are common in springs, this modulus is indeed a key factor in determining how the spring will stretch under a given load.

Reason (R): "A coil spring of copper has more tensile strength than a steel spring of the same dimensions."

The reason is incorrect. Steel generally has a higher tensile strength compared to copper. Tensile strength is the maximum stress that a material can withstand while being stretched or pulled before breaking. For structural applications, steel is preferred because of its superior tensile strength compared to copper.

Given the analysis, the correct response is that the Assertion (A) is correct but Reason (R) is incorrect.

Thus, the appropriate answer is: Statement I is correct and Statement II is incorrect.

The longitudinal stress at any point of cross-sectional area in a wire stretched by a weight is defined as the force applied per unit area. Stress is given by the formula:

Here, the force acting on the wire is the weight , and the area over which this force is distributed is the cross-sectional area . Therefore, the correct expression for the longitudinal stress in this scenario is .