Answer: 18 J.
- A 4 J
- B 18 J
- C 36 J
- D 100 J
Correct answer: B. 18 J
Explanation: KE_initial = (1/2)(2)(100) = 100 J. KE_final = (1/2)(2)(64) = 64 J. Loss = 100 - 64 = 36 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.