A spherical ball of density $\mathrm{\rho }$ and radius $0.003 \mathrm{m}$ is dropped into a tube containing a viscous fluid up to the $0 \mathrm{cm}$ mark as shown in the figure. Viscosity of the fluid $=1.26 \mathrm{N}·\mathrm{s}/{\mathrm{m}}^2$ and its density ${\mathrm{\rho }}_{\mathrm{L}}=\frac{\mathrm{\rho }}{2}=1260 \mathrm{kg}/{\mathrm{m}}^3$. Assume that the ball reaches a terminal speed at $10 \mathrm{cm}$ mark. The time taken by the ball to travel the distance between the $10 \mathrm{cm}$ and $20 \mathrm{cm}$ mark is $\left(\mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2\right)$