Sol. $k_{e q}=\frac{2 k \cdot k}{3 k}+k=\frac{5 k}{3}$ Angular frequency of oscillation $(\omega)=\sqrt{\frac{\mathrm{k}_{\mathrm{eq}}}{\mathrm{m}}}$ $$ (\omega)=\sqrt{\frac{5 \mathrm{k}}{3 \mathrm{~m}}} $$ Period of oscillation $(\tau)=\frac{2 \pi}{\omega}=2 \pi \sqrt{\frac{3 \mathrm{~m}}{5 \mathrm{k}}}$ $$ =\pi \sqrt{\frac{12 \mathrm{~m}}{5 \mathrm{k}}} $$