A commuter train passes a passenger platform at a constant speed of 42.9 m/s. The train horn is sounded at its characteristic frequency of 320 Hz.
(a) What overall change in frequency is detected by a person on the platform as the train moves from approaching to receding? (Indicate whether the frequency increases of decreases with the sign of your answer.)
(b) What wavelength is detected by a person on the platform as the train approaches?