Two objects of masses 200g and 500g have velocities of 10i m/s and (3i + 5 j)m/ s respectively. The velocity of their centre of mass is

• A

  5i - 25 j

• B

  $\frac{5}{7}\mathrm{i}-25\mathrm{j}$

• C

  $5\mathrm{i}+\frac{25}{7}\mathrm{j}$

• D

  $25\mathrm{i}-\frac{5}{7}\mathrm{j}$