Verified Solution • 2025–26 Session
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Q5.14: NCERT Physics - Part 1 WORK, ENERGY AND POWER 5.14 Solution: A molecule in a gas container hits a horizontal wall with speed …
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often think the molecule’s momentum changes direction, so momentum isn’t conserved for the molecule alone. Remember that momentum conservation applies to the whole system ($ ext{molecule}+ ext{wall}$); the wall receives an equal and opposite impulse, keeping total momentum constant. Likewise, an elastic collision requires kinetic energy conservation for the entire system, not just the molecule.
A molecule in a gas container hits a horizontal wall with speed 200 m s__ and angle 30� with the normal, and rebounds with the same speed. Is momentum conserved in the collision? Is the collision elastic or inelastic?
Step-by-Step Verified Solution
**Answer:** Momentum is conserved. The collision is elastic.
**Step-by-Step Explanation:**
The molecule rebounds with the same speed and angle, so kinetic energy is conserved. Hence, the collision is elastic.
Momentum is conserved (the wall recoils slightly, but its mass is so large that its recoil is negligible).
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