In what direction relative to the direction of travel can a force act on a car (traveling on level ground), and not change the kinetic energy? Can you give examples of such forces?
Forces that are perpendicular to the car will not change it's kinetic energy.
This is College Physics Answers with Shaun Dychko. Any force that is perpendicular to the direction of travel will not change the kinetic energy of the car. So the car is moving to the right horizontally. Gravity is perpendicular to it and so it will not change the kinetic energy. Likewise normal force also will not change the kinetic energy because these forces are not doing any work since their direction of the force is perpendicular to the displacement of the car.