A train travelling along a railway track in a straight line has a whistle that emits sound continuously at frequency $f$. A woman standing beside the track hears a sound with frequency $0.85f$. The speed of sound in air is $340\,\text{m s}^{-1}$. What is the train’s velocity?
- A$51\,\text{m s}^{-1}$ away from the woman
- B$51\,\text{m s}^{-1}$ towards the woman
- C$60\,\text{m s}^{-1}$ away from the woman
- D$60\,\text{m s}^{-1}$ towards the woman