If a car is accelerating at 3 m/s², what kind of force is acting on it?

When a car is accelerating at 3 m/s², this acceleration indicates that there is a net external force acting on the car. According to Newton's second law of motion, the net force acting on an object is equal to the mass of the object multiplied by its acceleration (F = m * a). In this context, the net external force is the total force resulting from all acting forces, which causes the car to accelerate at a specific rate.

The term "net external force" encompasses all the forces that are acting on the car (including engine force, friction, air resistance, etc.) and is what results in the observed acceleration. It is important to distinguish this from other types of forces mentioned in the choices; for instance, a constant force implies a steady value that does not change, while a variable force would mean the force changes over time. Neither of these definitions fits the situation unless stated otherwise.

In summary, the acceleration of the car at a given rate indicates that a net external force is indeed acting on it, which is responsible for its acceleration.