Answer: 20 m/s.
- A 10 m/s
- B 20 m/s
- C 14 m/s
- D 200 m/s
Correct answer: B. 20 m/s
Explanation: Using energy: mgh = (1/2)mv<sup>2.</sup> v = sqrt(2gh) = sqrt(2 x 10 x 20) = sqrt(400) = 20 m/s.
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.