Two objects of masses $m$and $4 m$ are at rest at an infinite separation. They move towards each other under mutual gravitational attraction. $G$ is the universal gravitational
constant. Then at separation $r:$

Initially potential and kinetic both energies are zero and from conservation of mechanical energy total enegy of the two objects is zero. Further, decrease in gravitational potential energy = increase in kinetic energy

or  $\frac{G\left(m\right)\left(4m\right)}{r}=\frac{1}{2}\mu {\nu }_r^2 ...\left(i\right)$

Here, $\mu =$reduced mass $= \frac{\left(m\right)\left(4m\right)}{m+4m}=\frac{4m}{5}$

Substituting in eq.(i), we get

${\nu }_r=$relative velocity of approach

          $= \sqrt{\frac{10Gm}{r}}$

From eq.(1) total kinetic energy

          $= \frac{G\left(m\right)\left(4m\right)}{r}=\frac{4G{m}^2}{r}$

Net torque of two equal and opposite forces acting on two objects is zero about any point. Therefore, angular momentum will remain conserved. Initially both the objects were stationary i.e., angular momentum about any point was zero. Hence, angular momentum of both the particles about any point will be zero at all instants.