Answer: 400 J.
- A 200 J
- B 400 J
- C 600 J
- D 1000 J
Correct answer: B. 400 J
Explanation: Initial KE = (1/2)(1)(400) = 200 J. PE = mgh = 1 x 10 x 20 = 200 J. Total final KE = 200+200 = 400 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.