1. The problem statement, all variables and given/known data A French and a U.S. submarine are moving directly towards each other during manoeuvres in still water. The French submarine is moving at 50.0 km.hr-1. It sends out a sonar signal at 1100.0 Hz. The frequency detected by the French submarine (reflected back from the U.S. submarine) is 1222 Hz. How fast is the U.S. submarine travelling towards the French submarine? Assume the velocity of sound in sea water is 1500 ms-1. 2. Relevant equations 3. The attempt at a solution Im thinking that the us submarine becomes a "virtual source" and that i have to solve this in two parts????? I need some help getting started(and finishing probably). Thanks to any helpers.