A spherical solid ball of volume V is made of a material of density $p_1$. It is falling through a liquid of density $P_2(p_2 <p_1)$. Assume that the liquid applies a viscous force on the ball that is proportional to the square of its speed v, i.e., $F_{viscous} = -kv^2(k>0).$ The terminal speed of the ball is
