If you were trying to build a sound proof room, which of the following materials would you choose in order to absorb the most sound, based on the coefficient of absorption for each material

It is really hard for me right know

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

What type of force holds atoms together in a crystal?