$v = \omega \sqrt {{a^2} - {x^2}} $
$= \frac{{2\pi }}{T}\sqrt {{A^2} - \frac{{{A^2}}}{4}} $
$= \frac{{2\pi }}{T}\sqrt {\frac{{3{A^2}}}{4}}$
$= \frac{{\pi A\sqrt 3 }}{T}$.

$y = 0.2\sin \left( {10\pi t + 1.5\pi } \right)\cos \left( {10\pi t + 1.5\pi } \right)$
The motion of particle is