= Solution
Use a year of $365.25$ days, so $t=9.46728\times10^8\,\mathrm s$, and $k=\rho A=10^{-11}\,\mathrm{kg\,m^{-1}}$. With $M_p=722\,\mathrm{kg}$ and $v_\infty\simeq1.752\times10^4\,\mathrm{m\,s^{-1}}$, <11/e> gives
$$
\boxed{M_f\simeq872\,\mathrm{kg},\qquad v_f\simeq14.5\,\mathrm{km\,s^{-1}}.}
$$
The corresponding cloud thickness is $x_f=(M_f-M_p)/k\simeq1.50\times10^{13}\,\mathrm m$. Checking $M_fv_f=M_pv_\infty$ verifies <conservation of momentum>; using the initial <speed> for all thirty years would overestimate the collected <mass>.
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