Two train carriages, each of mass $5000\,\text{kg}$, move towards each other on a horizontal frictionless track. One carriage is moving at $2.00\,\text{m s}^{-1}$ and the other at $1.00\,\text{m s}^{-1}$, as shown. They collide and stick together. Calculate the kinetic energy lost during the collision.
- A$1250\,\text{J}$
- B$7500\,\text{J}$
- C$11\,250\,\text{J}$
- D$12\,500\,\text{J}$