A person driving at v = 15 m/s crosses the line connecting two radio transmitters at right angles, as shown in the figure (d1 = 300 m and d2 = 100 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.
The image: http://www.webassign.net/walker/28-31alt.gif
(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 (a).
l2 - l1 = (m-1/2)(lambda)
The Attempt at a Solution
For part a I got 200 m.
Part B is where I have a problem. I know I need to get the vertical distance and use v = 15 m/s to find the time. Using triangles formed by connecting the vertical distance x to each radio transmitter I have made l2 = (x^2+100^2)^(1/2) and l1 = (x^2 + 300^2)^(1/2). When I subtract both of them and make them equal to 1/2lambda my x's cancel out, :-(.