Final answer:
The force of friction acting on the car is 150 N as it balances the 150 N force applied by the car's engine to maintain a constant velocity.
Step-by-step explanation:
The force of friction acting on a car traveling down the road at a constant velocity of 15 m/s when the car's engine applies a force of 150 N to propel the car forward is also 150 N. This is because when an object moves with a constant velocity, the net force acting on it is zero according to Newton's first law of motion. Therefore, the force of friction must balance the force applied by the car's engine. The forces are equal in magnitude but opposite in direction.