A stationary listener on a windless day hears the whistles of two identical freight trains approaching on parallel tracks. Each whistle has a rest frequency of 540Hz. Train X moves toward the listener at 32ms−1 while Train Y moves toward the listener at 18ms−1. The speed of sound in air is 340ms−1.
(a) Calculate the frequency heard from Train X.
(b) Calculate the frequency heard from Train Y.
(c) Determine the beat frequency the listener hears as the two sounds arrive simultaneously.
(d) After both trains have passed and are moving directly away from the listener at the same respective speeds, calculate the new beat frequency and compare it with the value obtained in part (c).