A spherically symmetric gravitational system of particles has a mass density $$ \rho=\left\{\begin{array}{l} \rho_0 \text { for } r \leq R \\ 0 \text { for } r>R \end{array}\right. $$ where $\rho_0$ is a constant. A test mass can undergo circular motion under the influence of the gravitational field of particles. Its speed $V$ as a function of distance $r( 0 < r < \infty )$ from the centre of the system is represented by