Mechanical Properties of Solids — Class 11 MCQs with Answers

Mechanical Properties of Solids — important questions & MCQs with answers (Class 11 Physics)

13 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 53 are timed and scored when you sign in.

1. Q1Easy

   SI unit of stress:

   A.Joule

   B.Pascal (N/m²)✓ Correct

   C.Newton

   D.Dimensionless

   Answer: B. Pascal (N/m²)

   Explanation: Stress is defined as force divided by area (σ = F/A), so its SI unit is the pascal (N/m²) — not the newton (N), which is just the force part, missing the area denominator.

2. Q2Easy

   Stress = ?

   A.Force only

   B.Force × Area

   C.Force / Area✓ Correct

   D.Area only

   Answer: C. Force / Area

   Explanation: Stress is force acting per unit cross-sectional area, σ = F/A (N/m²) — not force alone, and not force multiplied by area, which would give completely different units.

3. Q3Easy

   Strain is:

   A.Pressure

   B.Force/Area

   C.Force × length

   D.Dimensionless ratio of change in dimension to original✓ Correct

   Answer: D. Dimensionless ratio of change in dimension to original

   Explanation: Strain is the dimensionless ratio of the change in a dimension to its original value (ε = ΔL/L) — force×length has units of energy/torque, not strain, so it can't be the answer.

4. Q4Easy

   Hooke's law: stress ∝ strain (within elastic limit). Proportionality constant:

   A.Force

   B.Pressure

   C.Modulus of elasticity✓ Correct

   D.Density

   Answer: C. Modulus of elasticity

   Explanation: In Hooke's law, stress ∝ strain within the elastic limit, and the constant of proportionality is the modulus of elasticity (Young's, bulk, or shear modulus) — not pressure or density.

5. Q5Easy

   Young's modulus Y = ?

   A.Longitudinal stress / longitudinal strain✓ Correct

   B.Shear / volumetric

   C.Force / Area

   D.Strain

   Answer: A. Longitudinal stress / longitudinal strain

   Explanation: Young's modulus is specifically longitudinal stress divided by longitudinal strain, Y = σ/ε, for stretching along one direction — the shear or volumetric ratio instead defines shear or bulk modulus.

6. Q6Medium

   Wire of cross-section 2 mm² supports 100 N. Stress:

   A.50 Pa

   B.100 Pa

   C.5 × 10⁷ Pa✓ Correct

   D.2 × 10⁷ Pa

   Answer: C. 5 × 10⁷ Pa

   Explanation: Convert area first: 2 mm² = 2×10⁻⁶ m². Stress = F/A = 100/(2×10⁻⁶) = 5×10⁷ Pa. Forgetting to convert mm² to m² (leaving A = 2×10⁻³) is the trap behind a wrong power of ten.

7. Q7Medium

   Rod of length 2 m stretches by 1 mm. Strain:

   A.Cannot compute

   B.2 × 10⁻³

   C.0.5

   D.5 × 10⁻⁴✓ Correct

   Answer: D. 5 × 10⁻⁴

   Explanation: Convert 1 mm to 0.001 m, then strain = ΔL/L = 0.001/2 = 5×10⁻⁴. Inverting the ratio to L/ΔL instead of ΔL/L is the trap that produces a much larger, wrong value.

8. Q8Medium

   Wire (L = 2 m, A = 1 mm²) stretches 1 mm under 200 N force. Y:

   A.4 × 10¹¹ Pa✓ Correct

   B.2 × 10¹¹ Pa

   C.8 × 10¹¹ Pa

   D.1 × 10¹¹ Pa

   Answer: A. 4 × 10¹¹ Pa

   Explanation: Convert both mm values to metres: A = 1×10⁻⁶ m², ΔL = 1×10⁻³ m. Then Y = FL/(AΔL) = (200×2)/(10⁻⁶×10⁻³) = 4×10¹¹ Pa — mixing up A and ΔL in the denominator produces the other values.

9. Q9Medium

   Bulk modulus of water ≈

   A.2 × 10¹¹ Pa

   B.2 × 10⁹ Pa✓ Correct

   C.10⁶ Pa

   D.Variable

   Answer: B. 2 × 10⁹ Pa

   Explanation: Water's bulk modulus is about 2×10⁹ Pa — far higher than a gas, which compresses easily, but roughly a hundred times smaller than steel's (~2×10¹¹ Pa), so water is only mildly compressible.

10. Q10Medium

    Shearing strain in a body is related to shear modulus as:

    A.Cannot relate

    B.Strain · modulus

    C.Stress + modulus

    D.Shear strain = shear stress / shear modulus✓ Correct

    Answer: D. Shear strain = shear stress / shear modulus

    Explanation: Shear follows the same Hooke's-law pattern as tension: shear stress = shear modulus × shear strain, so rearranged, shear strain = shear stress ÷ shear modulus, not the modulus multiplied by strain.

11. Q11Hard

    Hooke's law is valid:

    A.Always

    B.Within proportional/elastic limit✓ Correct

    C.In plastic region only

    D.Never

    Answer: B. Within proportional/elastic limit

    Explanation: Hooke's law (stress ∝ strain) holds only within the proportional/elastic limit; beyond that point strain grows faster than stress and permanent plastic deformation sets in, so 'always' is wrong.

12. Q12Hard

    For wire of radius r, length L, stretched by mass m: stress =

    A.mgL

    B.mg/(πr²)✓ Correct

    C.mg·r

    D.Variable

    Answer: B. mg/(πr²)

    Explanation: The weight mg is the stretching force, and the wire's circular cross-section has area πr², so stress = F/A = mg/(πr²) — using diameter instead of radius in the area formula is the usual slip.

13. Q13Hard

    Y = (F·L)/(A·ΔL). Increasing length doubles ΔL keeping F, A same. New Y:

    A.Halves

    B.Doubles

    C.Same (material property)✓ Correct

    D.Variable

    Answer: C. Same (material property)

    Explanation: Young's modulus depends only on the material, not the specimen's dimensions — doubling the length also doubles ΔL proportionally (F, A, Y unchanged), so Y itself stays exactly the same.

Mechanical Properties of Solids — FAQs

More Class 11 Physics chapters

• 01Physical World
• 02Units and Measurements
• 03Motion in a Straight Line
• 04Motion in a Plane
• 05Laws of Motion
• 06Work, Energy and Power

Class 11 — other subjects

• Class 11 Biology chapters
• Class 11 Chemistry chapters
• Class 11 Computer Science chapters
• Class 11 English chapters
• Class 11 Mathematics chapters