Question

The Young’s modulus of a perfectly rigid body is

• A. unity
• B. zero
• C. infinity
• D. some finite non-zero constant

Answer 1

Answer: (C)

From Hooke's law, Young modulus $Y=\frac{\text{ Stress }}{\text{ Strain }}$
The Strain produced in a perfectly rigid body is zero
i.e Strain $=0$
$\therefore Y=\frac{\text{ Stress }}{0}$
$\Rightarrow Y=\infty$
Thus the Young's modulus of perfectly rigid body material is infinite.