Answer: All of the above.
- A mgh
- B mgh + mu x mg x cos(theta) x (h/sin(theta))
- C mgh(1 + mu/tan(theta))
- D All of the above
Correct answer: D. All of the above
Explanation: Both mgh + mu.mg.cos(theta).l = mgh + mu.mg.cot(theta).h = mgh(1 + mu/tan(theta)). All 3 expressions are equivalent.
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.