Impact and Collisions — Behavior of Elastic Bodies When two elastic bodies collide, which of the following occurs during the impact process?
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AThe two bodies will momentarily come to rest after collision
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BThe two bodies tend to compress and deform at the surface of contact
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CThe two bodies begin to regain their original shape
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DAll of the above
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E—
Answer
Correct Answer: All of the above
Explanation
Introduction / Context: Collision of elastic bodies is described by phases of compression and restitution. Even “rigid” bodies deform locally at the contact region; elasticity allows them to store and release strain energy, which governs their post-impact velocities.
Given Data / Assumptions:
- Elastic bodies with nonzero contact compliance.
- Short collision duration; external forces like weight are negligible during impact.
- Coefficient of restitution e ≤ 1; for perfectly elastic, e = 1.
Concept / Approach: The impact has two stages: compression (bodies deform, relative approach decreases) and restitution (bodies recover shape, relative separation increases). At the instant of maximum compression, relative velocity at the contact becomes zero; then restitution begins.
Step-by-Step Description:
Compression: contact stresses cause local deformation; kinetic energy partially stores as strain energy. At peak compression: relative velocity at contact is zero; the bodies may be momentarily at rest in certain frames and configurations. Restitution: stored strain energy drives separation; shapes are largely recovered for elastic bodies.Verification / Alternative check: Newton’s impact law relates separation and approach speeds: v_separation = e * v_approach. For e close to 1, recovery is nearly complete, matching the described behavior.
Why Other Options Are Wrong: Taken individually, (a) can be misread; however, together the options describe the full cycle (deform, pause at max compression, recover). Hence 'All of the above' best captures the correct sequence.
Common Pitfalls: Assuming perfectly rigid contact (no deformation); confusing zero relative speed at maximum compression with zero absolute speed in every frame.
Final Answer: All of the above — the deformation and recovery phases occur in elastic collisions, with a momentary stop at peak compression in the contact frame.