The Shinkansen, the Japanese bullet train, runs at high speed from Tokyo to Nagoya. Riding on the

Question:

The Shinkansen, the Japanese "bullet" train, runs at high speed from Tokyo to Nagoya. Riding on the Shinkansen, you notice that the frequency of a crossing signal changes markedly as you pass the crossing. As you approach the crossing, the frequency you hear is ƒ; as you recede from the crossing the frequency you hear is 2ƒ>3. What is the speed of the train?