We know that $x=a \sin \omega t$ $...(1)$
Where $x$ is displacement and a is amplitude.
Velocity $=\frac{d x}{d t}=a \omega \cos \omega t$
$=a \omega \cos (-\omega t)=a \omega \sin \left(\frac{\pi}{2}-(-\omega t)\right)$
$=a \omega \sin \left(\omega t+\frac{\pi}{2}\right)$ $...(2)$
From equation $( 1 )$ and $(ii)$ it is clear that
Velocity is ahead of displacement $(x)$ by $\frac{\pi}{2}$ angle.
$(A)\;y= sin\omega t-cos\omega t$
$(B)\;y=sin^3\omega t$
$(C)\;y=5cos\left( {\frac{{3\pi }}{4} - 3\omega t} \right)$
$(D)\;y=1+\omega t+{\omega ^2}{t^2}$