A high-performance sports car can go from 0 to 100 mph in 7.8 s. (Assume the car travels in the positive direction. Indicate the direction with the sign of your answer.)
(a) What is the car's average acceleration (in SI units; meter-kilogram-second)?
(b) The same car can come to a complete stop from 28 m/s in 5.5 s. What is its average acceleration?