In a test laboratory, an electric engine is used to accelerate a wheel from rest. The center-of-mass of the wheel remains stationary at all times. The wheel's angular acceleration is in the counter-clockwise direction. It rotates through an angular distance ??, achieves a final angular speed ? and has a constant moment of inertia I. If you assume constant angular acceleration and ignore friction and air resistance, what is the average power output of the engine, expressed in terms of ??, ? and/or I?