Elasticity and Plasticity - UNSOLVED PRACTICE SET

Q7. Define elasticity and plasticity. Give one example of each from daily life.

Q8. What is meant by the elastic limit of a material? What happens when a body is stressed beyond this limit?

Q9. Distinguish between elastic deformation and plastic deformation. Can a material show both types of deformation?

Q10. In your school laboratory, a student stretches a spring by hanging different masses from it. The spring returns to its original length when masses up to 500 g are used, but remains permanently stretched when a 1 kg mass is hung. Explain this observation using the concepts of elastic limit and plastic deformation.

Q11. Why does a rubber band become warm when stretched rapidly and released? Is this behaviour elastic?

Q12. A copper wire and a steel wire of the same dimensions are stretched by the same force. Which one will show greater deformation? Which one is more elastic?

Q13. Explain the concepts of elasticity and plasticity with examples. Discuss the molecular basis of elastic behaviour in solids. Why do some materials (like steel) show nearly perfect elastic behaviour while others (like putty) show mainly plastic behaviour?

Q14. Describe the behaviour of a wire when it is gradually loaded and then unloaded:

(a) Within the elastic limit

(b) Beyond the elastic limit but below the breaking point

(c) At the breaking point

Draw stress-strain curves for each case and explain the significance of different regions.

Q15. Analyse the following materials and classify them as mainly elastic, plastic, or brittle: rubber band, steel spring, chewing gum, glass rod, copper wire, chalk piece. For each material, explain:

(i) What happens when a small force is applied

(ii) What happens when a large force is applied

(iii) Whether the deformation is temporary or permanent

(iv) A practical application based on its properties

Q16. In a school experiment, students test the elasticity of different materials by applying increasing loads:

Material A: Returns to original length for loads up to 10 N; breaks at 25 N

Material B: Returns to original length for loads up to 5 N; shows permanent deformation at 8 N; breaks at 15 N

Material C: Shows permanent deformation even at 2 N; breaks at 30 N

(a) Identify which material is most elastic, which is most ductile, and which is most brittle.

(b) Which material would be best for making a spring? Justify.

(c) Which material would be best for making safety wires that must not break easily? Justify.

(d) Sketch approximate stress-strain curves for all three materials on the same axes.

Q17. A 2 m long steel wire of cross-sectional area 2 mm² is loaded with a 50 kg mass. Young's modulus of steel = 2 × 10¹¹ N/m².

(a) Calculate the extension of the wire if the load is within the elastic limit.

(b) If the elastic limit corresponds to a strain of 0.001, calculate the maximum load the wire can bear elastically.

(c) What happens if a load of 100 kg is applied and then removed?

(d) Calculate the permanent deformation if any, assuming the wire yields at a strain of 0.002.

Q18. Design a school-level experiment to compare the elastic properties of rubber and steel. Your design should include:

(a) List of materials required

(b) Step-by-step procedure

(c) Observations to be recorded

(d) How to determine which material is more elastic

(e) Expected results and conclusions

(f) Two safety precautions