posted by Chris Adison .
I need help with this question.
A commuter train blows its horn as it passes a passenger platform at a constant speed of 55.0 m/s. The train horn sounds at a frequency of 350 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?