A body is elastic if it regains its original size and shape once a deforming force is removed, and plastic if it does not. The internal restoring force set up per unit area within a deformed body is called stress, , with SI unit (pascal) and the same dimensions as pressure. The resulting fractional change produced in the body's dimensions is called strain — a
Mechanical Properties of Solids
Class 116 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Stress, strain and Hooke's law
Exam focus: Hooke's law (stress ∝ strain) holds only up to the proportional limit — the elastic limit lies slightly beyond it, so a material can still spring back to shape over a small range where stress and strain aren't proportional.
Stress, Strain and Hooke's Law
Physics Wallah - Alakh Pandey
Covers stress, strain, elasticity and Hooke's law together, with Young's modulus introduced as a lead-in to the next subtopic.
PhysicsNEET 2023show ▾Let a wire be suspended from the ceiling (rigid support) and stretched by a weight attached at its free end. The longitudinal stress at any point of cross-sectional area of the wire is:
PhysicsNEET 2020show ▾The dimensions of stress are:
2. Young's, bulk and shear moduli; Poisson's ratio
Exam focus: Young's modulus and shear modulus are defined only for solids — a liquid or gas can't sustain a shape-restoring shear or tensile stress, so only the bulk modulus applies to fluids.
Thermal Stress, Strain and Poisson's Ratio
Physics Wallah - Alakh Pandey
Covers Poisson's ratio directly; basic Young's/bulk/shear modulus definitions are introduced in earlier videos of this same series rather than derived fresh here.
PhysicsNEET 2024show ▾The maximum elongation of a steel wire of 1 m length, if the elastic limit of steel and its Young's modulus are respectively and , is:
- A.0.4 mm
- B.40 mm
- C.8 mm
- D.4 mm✓
Solution
At the elastic limit, strain . Elongation m mm.
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Save for spaced revision (free account)PhysicsNEET 2022show ▾Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): The stretching of a spring is determined by the shear modulus of the material of the spring.
Reason (R): A coil spring of copper has more tensile strength than a steel spring of the same dimensions.
In the light of the above statements, choose the most appropriate answer from the options given below:
- A.(A) is false but (R) is true
- B.Both (A) and (R) are true and (R) is the correct explanation of (A)
- C.Both (A) and (R) are true and (R) is not the correct explanation of (A)
- D.(A) is true but (R) is false✓
The worked solution is part of a paid pack.
PhysicsNEET 2020show ▾A wire of length , area of cross-section , is hanging from a fixed support. The length of the wire changes to when mass is suspended from its free end. The expression for Young's modulus is:
3. Elastic potential energy
Exam focus: Elastic energy stored per unit volume of a stretched wire is ½ × stress × strain, which simplifies to ½Y(strain)² — the same ½ × force × extension logic as a spring, expressed through Young's modulus.
Elastic Potential Energy in a Stretched Wire
Physics Wallah - Alakh Pandey
Exact single-concept match — derivation and energy density formula for a stretched wire.