Answer: 50 J.
- A 50 J
- B 100 J
- C 40 J
- D 25 J
Correct answer: A. 50 J
Explanation: KE = p<sup>2</sup>/2m = (20)<sup>2</sup> / (2 × 4) = 400/8 = 50 J.
As a pendulum swings, total mechanical energy (KE+PE) stays constant: at the highest points A and C, all energy is potential (zero speed); at the lowest point B, all of that energy has converted into kinetic energy (maximum speed).
Concept context
Work-energy theorem, potential energy, conservation of energy, collisions.