Equation 17.7 states that, at distance r away from a point source with power Pav, the wave

Question:

Equation 17.7 states that, at distance r away from a point source with power Pav, the wave intensity is 1 = Pav / 4πr2 Study Figure 17.9 and prove that, at distance r straight in front of a point source with power Pav moving with constant speed vS, the wave intensity is
1 = Pav / 4πr2 (v ─vs / v)