Final answer:
The net force acting on the car-trailer system is 0 N since no external forces are specified, meaning the system is either at rest or moving at a constant velocity.
Step-by-step explanation:
To determine the net force acting on a car-trailer system, we must consider both the mass of the car and trailer and any forces acting on them. If the car is pulling the trailer, and there is no other information given about external forces such as friction or applied forces, we can assume that the net force is zero. This is because, in the absence of any other forces mentioned, we only have the internal tension force between the car and the trailer, which do not contribute to the net force of the system as they are internal forces.