Answer: 2125 W.
- A 1000 W
- B 2125 W
- C 2000 W
- D 2250 W
Correct answer: B. 2125 W
Explanation: P = rate of (PE + KE) = per second: mgh + (1/2)mv<sup>2</sup> = 10 x 10 x 20 + (1/2) x 10 x 25 = 2000 + 125 = 2125 W.
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.