A commuter train blows its horn as it passes a passenger platform at a constant speed of 30.0 m/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? Hz (b) What is the frequency observed by a person on the platform as the train recedes from him? Hz (c) What wavelength does the observer find in each case? m m