When the speed of car moving down the hill remains constant, its kinetic energy remains same. The gravitational potential energy is converted into internal energy of brake drums. This causes heating of brake drums.
When the bus is moving, the man is in state of motion along with the bus. The velocity of man´s body is equal to that of the bus. As soon as he gets down and touches the platforms, his feet become stationary while the upper part of body tends to move forward due to inertia of motion and thus he falls forward. Hence, the man getting out of a moving bus has to run in the direction of the bus for some distance.
Engineering