An automobile starts from rest at a traffic light, accelerates uniformly and attains a speed of 20 m/s in 5 s. It then continues at this speed for the next 15 s, after which the driver applies the brakes and the automobile decelerates uniformly to rest in 10 s.
Answer the following:
(i) Draw a velocity–time (v–t) graph for the entire motion on a common set of axes. Choose convenient scales and label all significant points.
(ii) Using your graph, determine the total distance travelled by the automobile from the instant it starts to the instant it stops.
(iii) Calculate the average speed of the automobile for the whole journey.