A car is speeding up and has an instantaneous speed of 14.2 m/s when a stopwatch reads 9.1 s. It has a constant acceleration of 1.8 m/s^2.
(a) What change in speed occurs between t = 9.1 s and t = 12.6 s?
(b) What is the speed when the stopwatch reads 12.6 s?
(a) 12.6 s is 3.5 s after t=9.1s. The speed will have increased 1.8 x 3.5 = 6.3 m/s at that time.
(b) Add the result of (a) to 14.2 m/s.