On a car moving at constant speed on a level road, which statement about net force is true?

• A. The net force acting on the car is zero.
• B. The net force equals the car's mass times its velocity.
• C. The net force is equal to friction only.
• D. The net force is determined by air resistance alone.

Answer: (A)

When a car moves at constant speed on a level road, its velocity isn’t changing, so its acceleration is zero. According to Fnet = m a, if a = 0 then the net force acting on the car must be zero. The net force is the sum of all horizontal forces on the car—forward driving force plus backward resistive forces like friction and air resistance. These can balance each other, so the car keeps a steady speed. It’s not that net force equals mass times velocity (that would be momentum), and it isn’t just equal to friction or just air resistance—the net force is the overall balance of all forces acting on the car.