Why elastic bodies rebound: understanding elastic collision behavior In the collision of two elastic bodies, which explanation best captures what happens during and after impact?

Introduction / Context:
Elastic collision theory explains how bodies interact when they strike each other or a surface and rebound. The microscopic basis is reversible deformation: bodies store strain energy during compression and release it during restitution, producing post-impact separation without permanent deformation (ideally).

Given Data / Assumptions:

• Bodies are assumed elastic (no permanent set).
• Impact is along a well-defined line of impact.
• External influences like friction and air resistance are negligible during the very short impact interval.

Concept / Approach:
During an elastic impact there are two phases: compression and restitution. The normal component of relative velocity reduces to zero at maximum compression (bodies are momentarily at rest relative to each other along the impact line), then reverses as elasticity drives them apart. The coefficient of restitution e quantifies how much of the approach speed is recovered as separation speed.

Step-by-Step Solution:

Verification / Alternative check:
Impulse–momentum analysis shows the integral of contact force over the impact interval equals the change in momentum; the sign reversal of relative velocity during restitution matches option selections a–c.

Why Other Options Are Wrong:

• Individual statements a, b, and c are each true but incomplete alone; together (option d) they fully describe the process.
• “None of the above” conflicts with well-established impact mechanics.

Common Pitfalls:
Assuming bodies never come to rest during impact; ignoring the two-phase nature; equating elasticity with no compression (compression is essential).

Final Answer:
All of the above