Rationale
Neither speed nor velocity changes.
When a runner maintains a constant pace, both speed and velocity remain unchanged throughout the final straightaway. Speed is a scalar quantity that measures how fast the runner is going, while velocity is a vector quantity that includes both speed and direction. Since the runner's pace is constant, there are no variations in either measurement.
A) Both velocity and speed change.
This choice implies that there is variation in the runner's pace, which contradicts the premise of maintaining a constant speed. If both speed and velocity were changing, the runner would be accelerating or decelerating, which is not the case here.
B) Speed changes, but velocity does not.
This option suggests that while the runner's speed fluctuates, their direction remains constant. However, maintaining a constant pace means that speed must remain consistent throughout the straightaway, making this choice incorrect.
D) Velocity changes, but speed does not.
This choice indicates that while speed remains constant, the runner's direction changes, thus altering velocity. However, since the runner is on a straightaway and maintaining a constant pace, both speed and direction remain unchanged, invalidating this option.
Conclusion
In the context of a runner maintaining a constant pace down a straightaway, it is clear that neither speed nor velocity changes. This constancy is fundamental to the definitions of these terms, as speed remains steady and the direction does not vary. Understanding this distinction is crucial for comprehending motion in physics, particularly in scenarios involving uniform motion.
