Calculating Thermal Energy from a Head-On Collision

[crisicola]

I've got a question on thermal energy:

Two railroad cars, each of mass 6500 kg and traveling 86 km/h, collide head-on and come to rest. How much thermal energy is produced in this collision?

Converted 86 km/h to m/s = 2.389 m/s
I assumed that KE converted all into thermal energy:
KE = 1/2 mv^2, but it doesn't turn out right.

Thank you beforehand for any help!

 

[Tide]

Check your conversion. Also, did you include the kinetic energy of both cars?