Runner 1 moves at 8 m s^-1 and is 40 m from finish. Runner 2 starts 50 m away with 6 m s^-1 and constant acceleration a. Both reach finish simultaneously. What is a?

1. t = 40 / 8 = 5 s. 2. 50 = 6 * 5 + 0.5 * a * 25 -> 20 = 12.5a -> a = 1.6 m s^-2.