A truck on a straight road starts from rest accelerating at 2.0 m/s2 until it reaches a speed of 20 m/s. Then the truck travels for 20 s at constant speed until the brakes are applied, stopping the truck in a uniform manner in an additional 5.0 s. (a) How long is the truck in motion? (b) What is the average velocity of the truck for the motion described? My answers: (a) From rest to speed of 20 m/s it takes 10 s. Add 20 s. Add 5.0 s.... equals 35 s. (b) I know average velocity is displacement divided by time. But, how do I calculate the displacement???