CAIE A-Level Physics AS 5.1.7 P Fv and Use It to Solve Problems Questions

The force resisting the motion of a car is proportional to the square of the car's speed. The magnitude of the force at a speed of $20.0 \mathrm{~m} \mathrm{~s}^{-1}$ is 800 N .

What useful output power is required from the car's engine to maintain a steady speed of $40.0 \mathrm{~m} \mathrm{~s}^{-1}$ ?