A spherical solid ball of volume $V$ is made up of material of density $\rho$. It is falling through a liquid of density $\sigma$ ($\sigma < \rho$). Assume that the liquid applies a viscous force on the ball that is proportional to square of the terminal speed $V_T$, $F = -K V_T^2$, $K > 0$, then the terminal speed of the ball is ($g$ = acceleration due to gravity)