Question 1

According to Hooke's law, stress is directly proportional to strain within which limit?

Accepted Answer

According to Hooke's law, within the elastic limit, the stress developed in a body is directly proportional to the strain produced in it ($	ext{Stress} \propto 	ext{Strain}$).

Question 2

What is the SI unit of Young's Modulus of elasticity?

Accepted Answer

Young's modulus is the ratio of longitudinal stress to longitudinal strain. Since strain is dimensionless, its SI unit is the same as stress, which is $	ext{N/m}^2$ or Pascal (Pa).

Question 3

Which of the following materials is the most elastic?

Accepted Answer

Steel is more elastic than rubber because for a given strain, steel requires a much greater restoring force/stress than rubber, resulting in a higher Young's modulus.

Question 4

The elastic potential energy stored per unit volume of a stretched wire is given by:

Accepted Answer

The elastic energy density (energy per unit volume) stored in a stretched wire is given by the formula: $u = \frac{1}{2} 	imes 	ext{Stress} 	imes 	ext{Strain}$.

Question 5

What is the value of Young's modulus for a perfectly rigid body?

Accepted Answer

For a perfectly rigid body, no strain is produced regardless of the applied force (Strain = 0). Since Young's Modulus $Y = \frac{	ext{Stress}}{	ext{Strain}}$, $Y = \frac{	ext{Stress}}{0} = \infty$ (Infinity).

Mechanical Properties of Solids