Answer: 36.75 J.
- A 26.5 J
- B 36.75 J
- C 49 J
- D 53 J
Correct answer: B. 36.75 J
Explanation: Momentum: p = 5x4 + 3x2 = 26 kg m/s. Total mass = 8 kg. v<sub>f</sub> = 26/8 = 3.25 m/s. KE = (1/2)(8)(3.25)<sup>2</sup> = 4 x 10.5625 = 42.25 J. Hmm, let me recheck: (1/2)(8)(10.5625) = 42.25 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.