A vehicle is travelling at a speed of $30.0\,\text{m s}^{-1}$ straight towards an observer who is stationary. The vehicle’s horn produces a sound with frequency $440\,\text{Hz}$. The speed of sound in air is $340\,\text{m s}^{-1}$. What is the frequency of the sound heard by the observer?
- A$401\,\text{Hz}$
- B$404\,\text{Hz}$
- C$479\,\text{Hz}$
- D$483\,\text{Hz}$