Question

a car is moving east along a straight, level road at a constant velocity. which forces form an action/reaction force pair?
o the force of the tires against the road and the force of the road on the tires
o the weight of the car and the force of the road pushing up on the car
o the force of the engine on the car and the force due to friction on the car
o the normal force on the car and the force of the car pulling on earth

Explanation:

To identify an action - reaction pair, we use Newton's Third Law, which states that for every action, there is an equal and opposite reaction, and the two forces act on different objects.

• Option 1: The force of the tires against the road (action, tire on road) and the force of the road on the tires (reaction, road on tire) are a pair. The first force acts on the road, the second on the tires, they are equal in magnitude, opposite in direction, and are a result of the interaction between the tire and the road.
• Option 2: The weight of the car (gravity, Earth on car) and the force of the road pushing up on the car (normal force, road on car) are not an action - reaction pair. They are both acting on the car (the same object) and are a balanced force pair (since the car is on a level road and moving at constant velocity, these two vertical forces balance), not an action - reaction pair.
• Option 3: The force of the engine on the car and the force due to friction on the car are both acting on the car (the same object) and are horizontal forces that balance (since the car is moving at constant velocity), so they are not an action - reaction pair.
• Option 4: The normal force on the car (road on car) and the force of the car pulling on Earth (gravity, car on Earth) are not an action - reaction pair. The normal force is a contact force between the road and the car, while the force of the car pulling on Earth is the gravitational force exerted by the car on Earth (the reaction to the Earth's gravitational force on the car, which is the weight of the car). The normal force and this gravitational force on Earth are not an action - reaction pair.

Answer:

A. the force of the tires against the road and the force of the road on the tires