At mean position; $t=0, \omega t=0, y=0, V=V_{\max }=a \omega$

$K . E .=K E_{\max }=\frac{1}{2} m \omega^{2} a^{2}$

At extreme position $: t=\frac{T}{4}, \omega t=\frac{\pi}{2}, y=A, V=V_{\min }=0$

$\therefore \quad K . E .=K E_{\min }=0$

Kinetic energy in $S H M, K E=\frac{1}{2} m \omega^{2}\left(a^{2}-y^{2}\right)$

$=\frac{1}{2} m \omega^{2} a^{2} \cos ^{2} \omega t$