An elevator moving upward with velocity 8m/s comes to rest uniformly in 4s.
(a) Taking upward as positive, calculate the acceleration and state its sign.
(b) Now choose downward as the positive direction. Write the velocity and acceleration at t=0 with their correct signs under this convention.
(c) For each sign convention, state whether the elevator is speeding up or slowing down during the 4s interval, and give one reason.