(c) When $t = \frac{T}{12},\ then\ x = A\sin{\frac{2\pi}{T} \times \frac{T}{12} = \frac{A}{2}}$
$KE = \frac{1}{2}\ mv^{2} = \frac{1}{2}\ m\omega^{2}(r^{2} - x^{2})$
$= \ \ \frac{1}{2}\ m\omega^{2}\left( A^{2} - \frac{A^{2}}{4} \right)$
$= \ \ \frac{3}{4}\left( \frac{1}{2}\ m\omega^{2}A^{2} \right)$
$PE = \frac{1}{2}\ m\omega^{2}x^{2} = \frac{1}{4}\left( \frac{1}{2}\ m\omega^{2}A^{2} \right)$
$\frac{KE}{PE} = \frac{3}{1}$