Final answer:
The car with a positive velocity of 56 m/s and a negative acceleration of -4 m/s2 is slowing down because the acceleration is acting in the opposite direction to its motion.
Step-by-step explanation:
If a car is traveling with a velocity of 56 m/s and experiences an acceleration of -4 m/s2, it is slowing down. When the acceleration is in the opposite direction of the velocity, this results in a decrease in speed, which is commonly referred to as deceleration. In this case, the car has a positive velocity (56 m/s) indicating it's moving forward, and a negative acceleration (-4 m/s2), which indicates that the force is acting in the opposite direction to the motion of the car, thereby reducing its velocity.
As an example, imagine a car initially moving at a velocity of +30 m/s and then coming to a stop, finally having a velocity of 0 m/s. The overall change in velocity here is -30 m/s (0 m/s - +30 m/s), so the acceleration responsible for this change must be negative, indicating that the car was slowing down. Similar to figure 2.15 Car A's scenario where positive acceleration leads to speeding up, a negative acceleration leads to slowing down.