Single correct · +4 / −1
In kinetic theory, collisions of molecules with the walls of the container are assumed to be:
- (a) perfectly inelastic
- (b) perfectly elastic
- (c) partially elastic
- (d) non-existent
Answer and solution
Answer (b) perfectly elastic
Solution
Physics sir · 4 steps
If wall hits drained energy, the gas would cool down on its own. It does not, so the hits are elastic.
- What the theory needs. A gas left alone in a container at constant temperature keeps the same total kinetic energy. Kinetic theory links temperature directly to the average kinetic energy of the molecules.
- Why elastic. In a perfectly elastic collision, kinetic energy is conserved. The molecule bounces off the wall with the same speed. Only its velocity component perpendicular to the wall reverses.
Δ p = m vₓ - (-m vₓ) = 2 m vₓ
- Pressure from this. This momentum change of 2mvₓ per hit, summed over all molecules, gives the pressure P = 1/3ρ v̅²̅. That derivation rests on the collision being elastic.
- So. Collisions with the walls are assumed to be perfectly elastic, option (b).
The idea to keep. Kinetic theory assumes perfectly elastic collisions, with walls and between molecules. Kinetic energy is conserved, temperature stays steady, and the 2mvₓ momentum change gives pressure.
Answer from the NTA final answer key. Solution by PrepWiser.