1. The problem statement, all variables and given/known data A plane flies directly over your head. When the plane is 45° above the horizon from your perspective, you hear a sonic boom. How fast is the plane flying? 2. Relevant equations Doppler effect for a receding source f- = fo / (1+Vsource/c) 3. The attempt at a solution Any help would be appreciated, I'm not sure where to start!