ρ V = ρ S l = \frac{η N t}{c Δ T} \Rightarrow v = \frac{η N}{c Δ T ρ S} \approx 1, 7 m / s

${\rho V = \rho Sl = \frac{\eta Nt}{c\Delta T}\quad\Rightarrow\quad v = \frac{\eta N}{c\Delta T\rho S} \approx {1,7}{m/s}}$