please answer this question with explanation

4. (05 points) A 5000kg freight car having a kinetic energy of 2500J and going at a speed of 1m/s crashes into an identical freight car approaching on the same track that is moving at a speed of 2m/s with a kinetic energy of 10,000J. When they collide and couple together, the amount of heat they produce is d. 1150J e. 1250J f. 7500J g. 11,250J h. 11,500J