If the equation of motion of a particle is given by $s(t)=A\cos(wt+d)$, the particle is said to undergo simple harmonic motion. Assume $0\leq d <\pi$.

(a) Find the velocity of the particle at time $t$.
(b) What is the smallest positive value of $t$ for which the velocity is 0? Assume that $w$ and $d$ are positive.

(a) $v(t) =$
(b) $t=$