Two particles of mass `m_(1) "and" m_(2)` are in space at separation `vecr` [vector from `m(1)` to `m_(2)`]. The only force that the two particles experience is the mutual gravitational pull. The force applied by `m_(1) "on" m_(2) "is" vecF `. Prove that `mu(d^(2)vecr)/(dt^(2)) = vecF` where `mu"(m_(1)m_(2))/(m_(1) + m_(2))` is known as reduced mass for the two particle system .