A train moves with a constant speed on a straight track. Its horn produces a sound with frequency $500\,\text{Hz}$. A person beside the track detects a sound with frequency $450\,\text{Hz}$. The speed of sound in air is $340\,\text{m s}^{-1}$. Determine the speed of the train and state whether it is moving towards or away from the person.
Physics 9702 · AS & A Level · Doppler effect for sound waves