Final answer:
Option C and D: The scenario describes acceleration, particularly deceleration, as the runner slows to a stop, representing a change in velocity to zero.
Step-by-step explanation:
The scenario in which the runner slowed to a stop when reaching the finish line is an example of acceleration (a). This is because acceleration refers to the rate of change of velocity, which includes both changes in magnitude (speed) and direction of velocity. In this case, the runner is decelerating, which is a form of acceleration wherein the magnitude of velocity decreases. The runner’s initial velocity decreases to zero at the finish line, demonstrating a negative acceleration or deceleration.
Deceleration is often used in everyday language to describe the process of slowing down; however, in physics, both speeding up and slowing down are described as acceleration, which can be positive or negative, respectively. Recall that velocity is a vector quantity - it has both magnitude and direction. Thus, when the runner comes to a stop, they experience a change in velocity to zero, which represents a deceleration, and this change in velocity is what is defined as acceleration in physics.