A spherical solid ball of volume $V is made of a material of density {\rho _1}. It is falling through a liquid of density {\rho _2}\left( {{\rho _2} < {\rho _1}} \right). Assume that the liquid applies a viscous force on the ball that is proportional to the square of its speed v, i.e., {F_{viscous}} = - k{v^2}\left( {k > 0} \right).$ The terminal speed of the ball is