Sorry, but this seems too strange to be true. Are you sure you didn't miss anything?
Particularly strange since moving train (i.e. vehicle) is about the most common way doppler effect is explained in textbooks- it's not like you need any big "eureka" moment to get to this solution either.
Particularly strange since moving train (i.e. vehicle) is about the most common way doppler effect is explained in textbooks- it's not like you need any big "eureka" moment to get to this solution either.