Problem 2.55 — Maxwell Distribution: Energy Distribution

Problem Statement

Solve the work-energy problem: Write the Maxwell distribution in terms of molecular energy $\varepsilon = \frac{1}{2}mv^2$ and find the most probable energy. The speed distribution $f(v)dv$ in terms of energy $\varepsilon$: since $\varepsilon = \frac{1}{2}mv^2$, $d\varepsilon = mv\,dv$, $v = \sqrt{2\varepsilon/m}$: $$g(\varepsilo

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 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Step 2 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Step 3 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Worked Calculation

$$g(\varepsilo

Given Information

  • Mass $m$, velocity $v$, height $h$, or other given quantities
  • Any forces doing work (conservative or non-conservative) as specified

Physical Concepts & Formulas

The Work-Energy Theorem states that the net work done on an object equals its change in kinetic energy: $W_{\text{net}} = \Delta KE$. For conservative forces (gravity, spring, electric), a potential energy function $U$ exists such that $W = -\Delta U$, and the total mechanical energy $E = KE + U$ is conserved. Non-conservative forces (friction, air drag) remove mechanical energy, converting it to thermal energy. The power delivered is $P = dW/dt = \vec{F}\cdot\vec{v}$.

  • $W = \vec{F}\cdot\vec{d} = Fd\cos\theta$ — work done by constant force
  • $KE = \frac{1}{2}mv^2$ — kinetic energy
  • $U_g = mgh$ — gravitational PE (near Earth’s surface)
  • $U_s = \frac{1}{2}kx^2$ — elastic PE
  • $W_{\text{net}} = \Delta KE = KE_f – KE_i$ — work-energy theorem
  • $E_i = E_f$ (when only conservative forces act)

Step-by-Step Solution

Step 1 — Identify all forces and whether they are conservative.

Step 2 — Apply conservation of energy (if no friction):

$$

$$

Step 3 — If friction acts:

$$

$$

Step 4 — Solve for the unknown (usually $v_f$ or $d$).

Worked Calculation

Substituting all values with units:

Ball of mass $m = 0.5\,\text{kg}$ dropped from $h = 10\,\text{m}$:

$$

Answer

$$\boxed{v_f = \sqrt{2g h}}$$

Physical Interpretation

Maxwell’s thermodynamic relations connect seemingly unrelated thermodynamic derivatives, allowing quantities that are hard to measure directly (like entropy changes at constant pressure) to be computed from measurable ones.


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