The elastic strain energy stored in a rectangular cantilever beam due to a bending moment M applied at the end is given by ($$σ_{max}$$​ is Maximum Bending Stress, V is Volume and E is Young’s Modulus)

Correct option is C

​$$\begin{aligned}&\textbf{1. Maximum bending stress:} \\&\sigma_{\text{max}} = \frac{M h}{2I} = \frac{6M}{b h^2} \\[1em]&\textbf{2. Strain energy in a beam:} \\&U = \int_0^L \frac{M^2}{2EI} \, dx = \frac{M^2 L}{2EI} \\[1em]&\textbf{3. Moment of inertia for rectangular section:} \\&I = \frac{b h^3}{12} \\[1em]&\text{Substituting into energy expression leads to:} \\&U = \frac{\sigma_{\text{max}}^2 \cdot V}{6E}\end{aligned}$$​​