[Mentor's note - This thread was moved here from a non-homework forum, therefore it does not use the template.] Hi guys Need some help answering questions about frequencies and calculating velocity. I'm given two frequencies: 470Hz for an approaching object, 440Hz for when the object is moving away. Velocity of the speed of sound is 343m/s. Work out the frequency of the sound at the object. The receiver is stationary. What formula do I use to work this out? And once that's been calculated, can velocity be calculated using this formula? fr = fs(v/(v – vs)) where fr is frequency heard by the receiver, fs is frequency from the sender, v is velocity of sound through air, and vs is velocity of the object. Any help is appreciated.