The drawing shows three situations-A, B, and C-in which an observer and a source of electromagnetic waves are moving along the same line. In each case the source emits a wave that has a frequency of 4.57 1014 Hz. The arrows in each situation denote velocity vectors of the observer and source relative to the ground and have the magnitudes indicated (v or 2v), where the speed v is 2.75 106 m/s. Calculate the observed frequency in each of the three cases.