An aircraft emits a sound with frequency of $30.0\,\text{Hz}$. The speed of sound in air equals $330\,\text{m s}^{-1}$. The aircraft is positioned directly in front of a stationary observer and moves in a straight line either towards the observer or away from the observer. The observer detects the aircraft’s sound at a frequency of $20.0\,\text{Hz}$. What is the aircraft’s speed and direction?
- A$110\,\text{m s}^{-1}$, away from observer
- B$110\,\text{m s}^{-1}$, towards observer
- C$165\,\text{m s}^{-1}$, away from observer
- D$165\,\text{m s}^{-1}$, towards observer