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Q5.8: NCERT Physics - Part 1 WORK, ENERGY AND POWER 5.8 Solution: Answer carefully, with reasons: (a) In an elastic collision of…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often incorrectly assume that total kinetic energy remains constant throughout the entire collision process. In reality, during the brief contact period, kinetic energy is temporarily converted into elastic potential energy due to deformation, meaning kinetic energy is only conserved before and after the collision, not during it.
Answer carefully, with reasons: (a) In an elastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e. when they are in contact)? (b) Is the total linear momentum conserved during the short time of an elastic collision of two balls? (c) What are the answers to (a) and (b) for an inelastic collision? (d) If the potential energy of two billiard balls depends only on the separation distance between their centres, is the collision elastic or inelastic?
Step-by-Step Verified Solution
**Answer:** (a) No (b) Yes (c) No, Yes (d) Elastic
**Step-by-Step Explanation:**
(a) During the collision, kinetic energy is temporarily converted into potential energy (elastic deformation). The total kinetic energy is conserved only before and after the collision.
(b) Total linear momentum is conserved at all times during the collision (no external force).
(c) For inelastic collision: kinetic energy is not conserved even after the collision; momentum is still conserved.
(d) If potential energy depends only on separation, the force is conservative, so the collision is elastic.
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