Final answer:
The race car's acceleration was 2.5 m/s², calculated by dividing the change in velocity (-5.0 m/s) by the time interval (2.0 s), yielding -2.5 m/s². The magnitude is taken as 2.5 m/s².
Step-by-step explanation:
To find the race car's acceleration, we can use the formula for average acceleration, which is a = ∆v / t, where ∆v is the change in velocity and t is the time over which the change occurs. In the provided scenario, the race car's speed decreases from 85.0 m/s to 80.0 m/s over 2.0 seconds, so the change in velocity is 80.0 m/s - 85.0 m/s = -5.0 m/s (a negative sign indicates a decrease in speed). Therefore, the average acceleration is a = (-5.0 m/s) / 2.0 s = -2.5 m/s². The negative sign here indicates deceleration, but since the question asks for the magnitude, we can report the answer as 2.5 m/s².