An object of mass $m$ moving at speed $5u$ runs into an object of mass $5m$ that is travelling in the same direction at speed $u$, and the two objects stick together. What is the speed at which they move together in the original direction?
- A$\frac{3}{10}u$
- B$u$
- C$\frac{6}{5}u$
- D$\frac{10}{6}u$