Answer: 21 J.
- A 15 J
- B 21 J
- C 24 J
- D 35 J
Correct answer: B. 21 J
Explanation: W = integral from x=0 to 3 of (2x+3) dx = [x<sup>2</sup> + 3x] from 0 to 3 = 9+9 = 18 J. Hmm, with (2x+3): at x=3 it is 9+9=18. Force has only x-component so y-displacement does no work. W = 18 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.