Solution
= Solution
The <Boltzmann distribution> factors between momentum and position. Normalizing the height factor gives
$$
\boxed{P(z<Z<z+dz)=\frac{\beta mg\,e^{-\beta mgz}}{1-e^{-\beta mgL}}\,dz,\qquad0<z<L.}
$$
In the tall-box limit this becomes $\boxed{\beta mg\,e^{-\beta mgz}\,dz}$ on $z\ge0$, an <exponential distribution> with scale height $k_BT/(mg)$.