Final answer:
The power needed to maintain a constant speed of 75 km/h can't be calculated with the information given. Power is calculated using force and velocity, but since no force value is provided, this calculation cannot be completed. Additional specific vehicle data and resistance force measurements are needed.
Step-by-step explanation:
To determine the power needed to keep the car traveling at a constant speed of 75 km/h, we first convert this speed to meters per second: 75 km/h = 20.83 m/s. To maintain a constant speed, the car's engine must apply a force to counteract drag and other resistance forces. Assuming that the force needed to overcome resistance during deceleration is the same as the force needed to maintain the constant speed, we can calculate this force.
The deceleration of the car as it slows down from 85 km/h (23.61 m/s) to 65 km/h (18.06 m/s) in about 6.0 seconds can be used to estimate the resistive force. Using the equation F = ma, where m is the mass of the car and a is the deceleration, the resistive force can be calculated. However, there's not enough information to directly calculate the force in this case, so instead, assuming there are no additional forces acting on the car other than those present during deceleration, we can estimate power using the car's weight, speed decrease, and time.
Power P can be calculated using the work-energy principle, where P = work done/time. For a car traveling at constant speed, work done is equal to the force required to overcome resistive forces multiplied by distance, and power is this work done per unit of time. Without the resistive force, we cannot calculate the power directly; however, car manufacturers typically provide this data for their vehicles, or it can be estimated from similar models or by using tools like dynamometers. Once the resistive force or power is known, it can then be converted into horsepower using the conversion 1 hp = 746 W.