[{"hint": "Use F = ma.", "answer": "F = 5 × 3 = 15 N", "question": "Calculate: A 5 kg object accelerates at 3 m/s². What force is acting on it?"}, {"hint": "What force opposes the ball's motion?", "answer": "Friction between the ball and grass slows it down until it stops.", "question": "Explain why a soccer ball eventually stops rolling on grass."}]