Two hypothetical planets of masses m_1 and m_2 are at rest when they are infinite distance apart. Because of the gravitational force they move…

Two hypothetical planets of masses $\displaystyle \mathrm{m}_1$ and $\displaystyle \mathrm{m}_2$ are at rest when they are infinite distance apart. Because of the gravitational force they move towards each other along the line joining their centres. What is their speed when their separation is 'd' ? (Speed of $\displaystyle \mathrm{m}_1$ is $\displaystyle v_1$ and that of $\displaystyle \mathrm{m}_2$ is $\displaystyle v_2$ )