a. Use the equations of motion to show that the kinetic energy of an object of mass m moving with velocity v is 1/2 mv² .    
b. A car of mass 800 kg accelerates from rest to a speed of 20 m s⁻¹ in a time of 6.0 s.
i. Calculate the average power used to accelerate the car in the first 6.0 s.
ii. The power passed by the engine of the car to the wheels is constant. Explain why the acceleration of the car decreases as the car accelerates.