Unless indicated otherwise, assume the speed of sound in air to be v = 344 m/s. A railroad train is traveling at 25.0 m/s in still air. The frequency of the note emitted by the locomotive whistle is 400 Hz. What is the wavelength of the sound waves (a) in front of the locomotive and (b) behind the locomotive? What is the frequency of the sound heard by a stationary listener (c) in front of the loco-motive and (d) behind the locomotive?
Solution 46E Assume the speed of sound in air to be v = 344 m/s. Train travelling at 25 m/s. Frequency emitted by locomotive whistle is f =0400 Hz. (a).wavelength in front of locomotive = v/f = ((344 m/s)/400 Hz)(1 0.25 m/s/344 m/s) = 0.798 m. (a).wavelength behind the locomotive = v/f = ((344 m/s)/400 Hz)(1 + 0.25 m/s/344 m/s) = 0.922 m. (c). Frequency heard in front of the loco-motive f = v/ f = 344 m/s/0.798 m f = 431.07 Hz (d). Frequency heard behind the loco-motive f = v/ f = 344 m/s/0.922 m f = 373.10 Hz