You need to solve for .
Since you assume the particle is moving in harmonic motion, having or would contradict that -- so you can safely assume that . Now all you have to solve is
1. 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. Find the velocity.
Answer: v(t) = -Bwsin(wt + δ)
2. When is the velocity = 0?
Can you please show me step-by-step how to find when the velocity = 0? Thanks.