The driver of a car slams on her brakes to avoid collidingwith

a deer crossing the highway. what happens to the car's

kineticenergy as it comes to rest?

Its dissipated by the brake.

Explanation:

Traditional brakes use friction to stop the wheels (or axis). This friction its dissipated in the form of heat. There are others mechanism to brake that don't dissipated the energy, they stored it. In electric cars (or hybrids), there are regenerative brakes, that store the kinetic energy as electrical energy.