Answer: Ball 1 stops, ball 2 moves forward.
- A Both move forward according to conventional understanding
- B Ball 1 moves, ball 2 stops in routine practice
- C Ball 1 stops, ball 2 moves forward
- D Both stop overall in most cases
Correct answer: C. Ball 1 stops, ball 2 moves forward
Explanation: In elastic head-on collision with equal masses, the moving ball stops and the stationary ball moves with the initial velocity.
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.