Final answer:
The auto moving at a steady speed on a straight level road is a case of Newton's first law of motion. Because it's not accelerating or decelerating, the net force on it is zero. The backward frictional force equals the forward force exerted by the auto's engine.
Step-by-step explanation:
The auto moving at a steady 50 mph down a straight level road is an example of an object in Newton's first law of motion, also known as the law of inertia. This law states that an object in motion will continue in motion at a constant velocity, and an object at rest will stay at rest, unless acted upon by an external force. If the car is moving at a steady speed and is not accelerating or decelerating, this indicates that the net force on the auto is zero. This is because the backward frictional force from the ground (opposing the car's forward motion) is equal to the forward force exerted by the car's engine. Therefore, the correct answer is A. Zero.
Learn more about Net Force