Answer: 2000 J.
- A 500 J
- B 1000 J
- C 2000 J
- D 3000 J
Correct answer: C. 2000 J
Explanation: W = efficiency x Q<sub>in</sub> = 0.4 x 5000 = 2000 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.