Sol. $$ \begin{aligned} & \mathrm{v}=\omega \sqrt{\mathrm{A}^2-\mathrm{x}^2} \\ & \text { at } \mathrm{x}=\frac{2 \mathrm{~A}}{3} \end{aligned} $$ $$ v=\omega \sqrt{A^2-\left(\frac{2 A}{3}\right)^2}=\frac{\sqrt{5} A \omega}{3} $$ New amplitude $=\mathrm{A}^{\prime}$ $$ \begin{aligned} & \mathrm{v}^{\prime}=3 \mathrm{v}=\sqrt{5} \mathrm{~A} \omega=\omega \sqrt{\left(\mathrm{A}^{\prime}\right)^2-\left(\frac{2 \mathrm{~A}}{3}\right)^2} \\ & \mathrm{~A}^{\prime}=\frac{7 \mathrm{~A}}{3} \end{aligned} $$