A French submarine and a U.S. submarine move toward each other during maneuvers in motionless water in the North Atlantic. The French sub moves at speed Vf, and the U.S. sub at speed Vus". The French sub sends out a sonar signal (sound wave in water) at 1.000 x10^3 Hz. Sonar waves travel at 5470 km/h. The U.S sub detects a frequency of 1022.140Hz. The French sub detects the signal reflected back to it by the U.S sub at a frequency of 1044.854Hz.
What are the speeds of the U.S. and the French subs? Identify which sub is the source and which one is the observer and show it in a sketch for each of the cases when the signal is detected by the U.S. sub and for when the signal is detected by the French sub. And then use the appropriate signs in the formula F ' = [(V± Vo)/(V± Vs)]f in each case.