Two \(5000-\mathrm{kg}\) freight cars roll toward one another (one at \(1 \mathrm{~m} / \mathrm{s}\) and the other at \(2 \mathrm{~m} / \mathrm{s}\) ) on a level track. Thus before they collide one car's kinetic energy is \(2500 \mathrm{~J}\) and the other's is \(10,000 \mathrm{~J}\). They collide and couple together. The amount of kinetic energy turned into heat (mostly warring the couplers) in the collision is ____________
