Vidaara.orgClass 11 · Physics
CodeVID-P11-08-SSH-01
Stress, Strain & Hooke's Law — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The dimensional formula of stress is:
- A.$[\text{ML}^{-1}\text{T}^{-2}]$
- B.$[\text{MLT}^{-2}]$
- C.$[\text{ML}^2\text{T}^{-2}]$
- D.$[\text{M}^0\text{L}^0\text{T}^0]$
2.
Which of the following is dimensionless?
- A.stress
- B.modulus of elasticity
- C.strain
- D.force
3.
A force applied normally and outward, increasing the length of a rod, produces:
- A.compressive stress
- B.tensile stress
- C.shear stress
- D.hydraulic stress
4.
The SI unit of stress is:
- A.N
- B.N/m
- C.N/m$^2$
- D.no unit
5.
Beyond the yield point, the deformation of a material is:
- A.fully elastic
- B.permanent (plastic)
- C.zero
- D.always brittle
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define stress and strain. State the SI unit of each.
7.
State Hooke's law and write its mathematical form.
8.
A wire of area $4\times10^{-6}\ \text{m}^2$ carries a load of 80 N. Find the stress.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Distinguish between tensile, compressive and shear stress with one example each.
10.
Draw and label the stress–strain curve for a ductile metal, marking the proportional limit, elastic limit, yield point and fracture point.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Explain the stress–strain curve obtained when a metal wire is gradually loaded to breaking point. Describe the elastic and plastic regions, and explain how the curve distinguishes ductile from brittle materials.
Answer Key
Section A — Multiple Choice Questions
- (A) $[\text{ML}^{-1}\text{T}^{-2}]$
- (C) strain
- (B) tensile stress
- (C) N/m$^2$
- (B) permanent (plastic)
Section B — Short Answer (2 marks)
- Stress is restoring force per unit area ($\text{N/m}^2$); strain is fractional deformation (dimensionless, no unit).
- Within the elastic limit, $\text{Stress}\propto\text{Strain}$, so $\frac{\text{Stress}}{\text{Strain}}=E$, the modulus of elasticity.
- $\text{Stress}=\frac{80}{4\times10^{-6}}=2\times10^{7}\ \text{N/m}^2$.
Section C — Short Answer (3 marks)
- Tensile: outward pull stretching a rod; compressive: inward push shortening a pillar; shear: tangential force sliding the top of a block over its base.
- Straight line up to the proportional limit (Hooke's law), then elastic limit, yield point (plastic region begins), ultimate strength, and finally the fracture point where it breaks.
Section D — Long Answer (5 marks)
- From O the curve is straight (Hooke's law) to the proportional limit; up to the elastic limit the wire recovers fully. Beyond the yield point it deforms plastically (permanent set) up to the ultimate strength, then fractures at the breaking point. A large plastic region (yield to fracture) marks a ductile material; a tiny one marks a brittle material.
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