3

Background
Let's say I have the $i$'th gas molecule with velocity $\vec v_i(t)$ at time $t$. To find the net displacement $s_i$ we integrate with respect to $t$:
$$ \vec s_i = \int_{0}^{t} \vec v_i(t') dt' $$
Since, the gas molecule under goes collisions. Initially the $i$'th gas molecule has ve...