Mechanical Properties of Solids for NEET UG
Why does a steel wire stretch so little and a rubber band so much? Stress, strain and elastic moduli answer that, and they decide how bridges, bones and cables are designed.
PhysicsClass 1161 MCQs2 lessons11 flashcards3 memory tricks
Practise Mechanical Properties of Solids free
What you'll learn
- Stress, strain and Hooke's law
Calculate stress and strain, and use Young's modulus to find how much a wire stretches. - The stress–strain curve
Read the stress–strain graph and tell ductile from brittle materials.
Key formulas
| Stress | σ = F/A (N/m² or Pa) |
|---|---|
| Longitudinal strain | ΔL/L (no unit) |
| Young's modulus | Y = (F/A)/(ΔL/L) = FL/(AΔL) |
Memory tricks
Elasticity means resisting deformation. Steel's Young's modulus (about 2 × 10¹¹ Pa) is far larger than rubber's, so steel is more elastic.
Proportional limit (Hooke's law ends), Elastic limit, Yield point, Ultimate tensile strength, Fracture point.
Poisson's ratio = lateral strain ÷ longitudinal strain. For most materials it lies between 0 and 0.5.
Try 3 NEET-style questions
Q1. A wire stretched by a force of 200 N extends by 1 mm. The elastic potential energy stored in it is
- 0.2 J
- 0.1 J
- 100 J
- 200 J
Show answer
Answer: (2) 0.1 J
U = ½ F ΔL = ½ × 200 × 10⁻³ = 0.1 J.
Q2. A rubber cube is subjected to a hydraulic pressure that reduces its volume by 0.1%. If the pressure is 10⁵ Pa, the bulk modulus of rubber is
- 10⁸ Pa
- 10⁵ Pa
- 10² Pa
- 10¹¹ Pa
Show answer
Answer: (1) 10⁸ Pa
B = p/(ΔV/V) = 10⁵ / 10⁻³ = 10⁸ Pa.
Q3. Liquids and gases possess
- only a bulk modulus
- only a Young's modulus
- only a shear modulus
- all three elastic moduli
Show answer
Answer: (1) only a bulk modulus
Fluids cannot sustain a fixed length or shape, so they have no Young's or shear modulus. They resist compression, so they have a bulk modulus.
Practise all 61 questions Free · explanations for every option · see where you go wrong