1. The problem statement, all variables and given/known data You are standing on the side of the Trans-Canada Highway as the Physicsmobile approaches you. As it approaches, you hear an engine noise of 1100 Hz. After it passes, you hear an engine noise of 950 Hz. How fast was the Physicsmobile travelling? 2. Relevant equations f2 = apparent frequency f1 = actual frequency emitted by source v = speed of sound in air vs = speed of source 3. The attempt at a solution I'm not sure how to re-arrange the formula. If I fill in all variables that I'm given, there are still two left blank (vs and f).