10 Two particles of masses `m_(1)` and `m_(2)` initially at rest start moving towards each other under their mutual force of attraction. The speed of the centre of mass at any time t, when they are at a distance r apart, is

Options

A. zero
B. `(G(m_(1)m_(2))/(r^(2)).(1)/(m_(1)))t`
C. `(G(m_(1)m_(2))/(r^(2)).(1)/(m_(2)))t`
D. `(G(m_(1)m_(2))/(r^(2)).(1)/(m_(1)+m_(2)))t`