Centripetal force direction in uniform circular motion

Steps:

• The truck moves at constant speed in a vertical circle, indicating uniform circular motion.
• Uniform circular motion requires centripetal acceleration directed toward the circle's center.
• The resultant force equals mass times centripetal acceleration, so it points toward the center.
• Arrow D aligns with this inward radial direction at the truck's position.

Why D is correct:

• Newton's second law (F_net = m v²/r) requires the net force to act toward the center for circular motion.

Why the others are wrong:

• A points upward (gravity direction), ignoring centripetal requirement.
• B points downward or tangential, which would cause linear or decelerating motion.
• C points radially outward, opposing the needed centripetal force.

Final answer: D