A fan uses a rotating blade to moves 2m3 of air each second at a speed of 3 m/s. Assumes air is initially at rest and has a density of 1 kg/m3. Fans are inefficient; assume an efficiency of 10%.

Which statement best describes the superposition principle? a.) if two in-phase waves arrive simultaneously at a point, their amplitudes add up b.) if two out-of-phase waves arrive simultaneously at a point, their amplitudes add up c.) if two in-phase waves arrive at a point one after another, their amplitudes add up d.) if two out-of-phase waves arrive at a point one after another, their amplitudes adds up