A particle moves according to the law of motion [math] where [math] is measured in seconds and [math] in feet.

a.) Find the velocity at time [math].
Answer:

b.) What is the velocity after [math] seconds?
Answer:

c.) When is the particle at rest? Enter your answer as a comma separated list. Enter None if the particle is never at rest.
Answer:

d.) When is the particle moving in the positive direction?
When [math] and [math]