Q. A person driving at v = 18 m/s crosses the line connecting two radio transmitters at right angles, as shown in the figure (d1 = 420 m and d2 = 140 m). The transmitters emit identical signals in phase with each other, which the driver receives on the car radio. When the car is at point A the radio picks up a maximum net signal.

(a) What is the longest possible wavelength of the radio waves?

(b) How long after the car passes point A does the radio experience a minimum in the net signal? Assume that the wavelength has the value found in part.