The drawing shows three situations — A, B, and C — inwhich an observer and a source of electromagnetic waves are movingalong the same line. In each case the source emits a wave that hasa frequency of 4.57 x 1014 Hz. The arrows in eachsituation denote velocity vectors of the observer and sourcerelative to the ground and have the magnitudes indicated(v or 2v), where the speed v is 2.8 x106 m/s. Calculate the observed frequency in each of the three cases.