Problem 2.11 — Mean Speed of Gas Molecules

Problem Statement

Find the mean speed of oxygen molecules at $T = 300\ \text{K}$.

Given Information

  • See problem statement for all given quantities.

Physical Concepts & Formulas

This problem applies fundamental physics principles to the scenario described. The solution requires identifying the relevant conservation laws and equations of motion, then solving systematically with careful attention to units and sign conventions.

  • See the step-by-step solution for the specific equations applied.
  • All quantities are in SI units unless otherwise stated.

Step-by-Step Solution

Step 1 — Identify given quantities and set up the problem: The Maxwell mean speed:

Step 2 — Apply the relevant physical law or equation: $$\bar{v} = \sqrt{\frac{8RT}{\pi M}} = \sqrt{\frac{8\times8.314\times300}{\pi\times0.032}} = \sqrt{\frac{19954}{0.10053}} = \sqrt{198,497} \approx 446\ \text{m/s}$$

Step 3 — Solve algebraically for the unknown: Result: $\bar{v} \approx 446\ \text{m/s}$.

Worked Calculation

$$\bar{v} = \sqrt{\frac{8RT}{\pi M}} = \sqrt{\frac{8\times8.314\times300}{\pi\times0.032}} = \sqrt{\frac{19954}{0.10053}} = \sqrt{198,497} \approx 446\ \text{m/s}$$

$$\text{Numerical result} = \text{given expression substituted with values}$$

$$\boxed{\bar{v} = \sqrt{\frac{8RT}{\pi M}} = \sqrt{\frac{8\times8.314\times300}{\pi\times0.032}} = \sqrt{\frac{19954}{0.10053}} = \sqrt{198,497} \approx 446\ \text{m/s}}$$

The Maxwell mean speed:

$$\bar{v} = \sqrt{\frac{8RT}{\pi M}} = \sqrt{\frac{8\times8.314\times300}{\pi\times0.032}} = \sqrt{\frac{19954}{0.10053}} = \sqrt{198,497} \approx 446\ \text{m/s}$$

Result: $\bar{v} \approx 446\ \text{m/s}$.

Answer

$$\boxed{\bar{v} = \sqrt{\frac{8RT}{\pi M}} = \sqrt{\frac{8\times8.314\times300}{\pi\times0.032}} = \sqrt{\frac{19954}{0.10053}} = \sqrt{198,497} \approx 446\ \text{m/s}}$$

Physical Interpretation

The numerical answer is physically reasonable — matching expected orders of magnitude and dimensional analysis. The result confirms the theoretical prediction and provides quantitative insight into the system’s behaviour.


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