Final answer:
The force of friction acting on a car cruising at 30.0 m/s with an engine force of 75.0 N is also 75.0 N, maintaining the car's constant speed.
Step-by-step explanation:
If a car is cruising on the highway at a constant speed of 30.0 m/s and the engine is applying a force of 75.0 N, we can infer that the force of friction acting against the car's motion is also 75.0 N. This conclusion is based on Newton's first law of motion which states that an object in motion will stay in motion with a constant velocity unless acted upon by a net external force. Therefore, in this scenario, where the car's velocity remains constant, the net force must be zero; this implies that the opposing forces—the force from the engine and the force of friction—are equal.