$A$ spherical solid ball of volume $V$ is made of a material of density $\rho_1$. It is falling through a liquid of density $\rho_2$ $(\rho_2 < \rho_1)$. 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

• A
  $\sqrt {\frac{{Vg\left( {{\rho _1} - {\rho _2}} \right)}}{k}}$
• B
  $\frac{{Vg{\rho _1}}}{k}$
• C
  $\sqrt {\frac{{Vg{\rho _1}}}{k}}$
• D
  $\frac{{Vg\left( {{\rho _1} - {\rho _2}} \right)}}{k}$