Physics
posted by Cooper .
Two ships in a heavy fog are blowing their horns, both of which produce sound with a frequency of 165.0 Hz One ship is at rest; the other moves on a straight line that passes through the one at rest.
If people on the stationary ship hear a beat frequency of 3.5 Hz, what is the speed of the approaching ship?
If people on the stationary ship hear a beat frequency of 3.5 Hz, what is the speed of the receding ship?

There are two possible received frequencies that would produce that beat frequency. One corresponds to the ships approaching each other and the other for when they are separating. They don't say clearly which case it is.
Assume they are approaching. In that case the received frequency is 168.5 Hz
Use the appropriate Doppler shift formula to compute the moving ship's velocity. Both cases should give NEARLY the same answer, about 7 m/s assuming a sound speed of 340 m/s. You will need to assume an air temperature to get an accurate sound speed.