Final answer:
When a pilot performs a vertical maneuver around a circle with a radius moving at constant speed, the centripetal force is zero.
Step-by-step explanation:
When a pilot performs a vertical maneuver around a circle with a radius (r) at constant speed, the following statement is true: d) Centripetal force is zero.
The centripetal force is the force that keeps an object moving in a circular path, directed toward the center of the circle. In this case, since the pilot is moving at a constant speed, there is no need for a centripetal force to maintain the circular motion. Therefore, the centripetal force is zero.