physics
posted by Anonymous .
A train whistle emits a sound with a frequency of 1000 Hz when standing in the station. If the same whistle is blown when it is moving away from the station at 40 mph what will be the approximate frequency someone standing at the station will hear?

You need to review the Doppler shift equations. They should be in your textbook or class notes, and are easily found onlkne.
You will also need to know the velocity of sound. Assume it is 340 m/s, which is 760 mph.
The frequency heard at the station will be less than 1000 Hz.
The answer will be about 950 Hz, but you should do the exact calculation yourself.