$v = \frac{{dx}}{{dt}} = - A\omega \sin \left( {\omega \,t + \frac{\pi }{4}} \right)$
For maximum speed, $\sin \,\left( {\omega \,t + \frac{\pi }{4}} \right) = 1$
==> $\omega \,t + \frac{\pi }{4} = \frac{\pi }{2}$ or $\omega \,t = \frac{\pi }{2} - \frac{\pi }{4}$
==> $t = \frac{\pi }{{4\omega }}$

where $x=$ displacement at time $t$
$\omega =$ frequency of oscillation
Which one of the following graphs shows correctly the variation $a$ with $t$ ?
Here $a=$ acceleration at time $t$
$T=$ time period
