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Two identical containers A and B each hold 1 mole of O2. Vessel A is at rest with pressure P0; vessel B moves at constant speed V0 and has pressure P. The rms speed of the gas molecules is the same in both vessels. Which of the following is correct?

1. P > P0
2. P < P0
3. P = P0
4. P = P0 * (V_rms² + V0²) / V_rms²

Correct answer: P = P0

Solution

The rms speed given is the thermal rms speed in the container's rest frame. Since both containers have the same n, V, and thermal rms speed (hence the same T), the pressure P = nRT/V is the same in both. The bulk velocity V0 does not affect internal pressure.

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