Answer: Negative.
- A Positive
- B Negative
- C Zero
- D Depends on surface
Correct answer: B. Negative
Explanation: Friction always opposes motion. Work done by friction = -f x d (negative, as force and displacement oppose).
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.