Physics make-up packetname_cle14. an observer hears a sound with a frequency of 400 hz. if the speed of sound is 340 m/s, what is the wavelength of the sound? a. 0.85 mb. 1.2 mc. 2.75 m13.6 m15. as sound travels from steel into air, its speed decreases. if the frequency of the wavedoesn't change, what happens to its wavelength? a. it increases(b) it decreasesc. it remains the samed. there is not enough information given