According to Newton's First Law of Motion, an object at rest will stay at rest, and an object in motion will remain in motion at a constant velocity unless acted upon by an external force.
Among the given options, the situation that requires an external force to change the object's state of motion is:
A car coming to a stop at a red light.
This is because it requires an external force (the brakes applied by the driver) to stop the car's motion.
The other situations (a satellite orbiting Earth, a person walking at a steady pace, and a horse running around a track) either involve constant motion or balanced forces that do not require a change in state unless acted upon by external forces.
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