A bus travelling at 15m/s undergoes two successive stages of uniform acceleration while moving on a straight road.
(i) First, the driver applies the brakes and the speed drops uniformly to 5m/s in 4s. Calculate the acceleration during this braking phase.
(ii) Immediately afterwards, the bus accelerates uniformly and reaches 20m/s in the next 6s. Calculate the acceleration during this speeding-up phase.
(iii) Determine the overall change in velocity of the bus from the beginning of braking to the end of the speeding-up phase.
(iv) Compute the average acceleration of the bus for the entire 10s interval considered.