1. The problem statement, all variables and given/known data A radio played on a moving train has frequency of 85 Hz. A second radio played at train station is at rest. What is the beat frequency heard if train approaches the station at 10 m/s? 2. Relevant equations f' = [f \ (1-vsource/vsound) I used this equation because the source is moving towards a stationary object. 3. The attempt at a solution f' = 85 \ (1 - 10\343) f' = 85\ 0.971 f' = 88 Hz The answer is 2.5. So, I think I'm missing a second equation. However, if the source is moving towards the object I assumed the question was asking what the beat freq. would be heard at the station.