Among the following, which is least elastic?
Try it first: pick an option, then read the explanation.
Correct answer: D. Rubber
Asked in SSC JE 22/01/2018 (Morning); SSC JE 2012
Detailed Explanation
In everyday speech rubber is ‘very elastic’ because it stretches a lot. In mechanics, ‘more elastic’ means a higher modulus of elasticity — more stress needed for a given strain.
Why “Rubber” Is Correct
Iron (≈ 200 GPa), copper (≈ 120 GPa) and silver (≈ 80 GPa) have very high moduli. Rubber's modulus is only a few MPa. So, in the engineering sense, rubber is the least elastic.
Why the Other Options Are Wrong
- A. Iron: Iron (steel) has the highest modulus of the four.
- B. Copper: Copper has a high modulus.
- C. Both copper and silver: Copper and silver are both far stiffer than rubber.
Key Point
In mechanics, elasticity is judged by E: higher E = more elastic. Rubber has the lowest.
Key Concepts for Students
- Steel is more elastic than rubber in this sense.
- Rubber has a large elastic range but a tiny E.
- E(steel)/E(rubber) is about 10⁵.
Practice more: this is question 39 in Stress and Strain MCQs – Part 3. Try the whole set and check every answer instantly.