If the equation of motion of a particle is given by s = b cos(ωt + δ), the particle is said to undergo simple harmonic motion.

(a) find the velocity of the particle at time t.

(b) when is the velocity 0?

SO for the first part, please use the formula:
v(t) = -Bω*sin(ωt+δ)
and you will get the result
For the part b, we have to take into account that velocity is 0 so
s= is said to be maximum so
s= max when v=0=-Bwsin(wt+d)
0=sin(wt+d) arc sin 0=0=(wt+d)
so -d=wt -d/w=t = time
Hope it helps

Sorry i don’t know what to do