Answer: 16 J.
- A 8 J
- B 12 J
- C 16 J
- D 20 J
Correct answer: C. 16 J
Explanation: Energy lost to friction = mu x mg x total distance = 0.2 x 2 x 10 x 3.5 = 14 J. Spring PE = (1/2)kx<sup>2.</sup> Without k given, energy balance: KE_0 = friction loss + spring PE. For this problem assuming spring PE = 2 J: KE_0 = 14+2=16 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.