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19. After crossing the finish line of a 100 meter dash, a runner quickly stops. In 3 seconds he goes from 9 m/s to a stop. Assume the acceleration is constant. a. Find his acceleration in these three seconds. (1 pt) b. How far must he travel in these three seconds? (1 pt) c. What is his velocity at 2 sec after he crosses the finish line? (1 pt)