(b) $\frac{U}{E} = \frac{\frac{1}{2}m\omega^{2}y^{2}}{\frac{1}{2}m\omega^{2}a^{2}} = \frac{y^{2}}{a^{2}} = \frac{\left( \frac{a}{2} \right)^{2}}{a^{2}} = \frac{1}{4} \Rightarrow U = \frac{E}{4}$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.