How big are the motions of air molecules?

Joe sings into a long cardboard tube of radius r = 0.2 m. He hits a perfect middle C (256 Hz), causing the air molecules to shake back-and-forth. At the far end of the tube, the sound wave carries a power of 0.01 Watt = 0.01 Joule/sec .

How large is the amplitude of motion of the air molecules in the tube?