A commuter train blows its horn as it passes a passenger platform at a constant speed of 40.0m/s. The train horn sounds at a frequency of 305 Hz when the train is at rest.
(a) What is the frequency observed by a person on the platform as the train approaches?
(b) What is the frequency observed by a person on the platform as the train recedes from him?
(c) What wavelength does the observer find in each case?