A pair of die-hard sports fans decide to ride their motorcycle to the local game, equipped with identical air horns. While stuck at a stoplight, one rider blasts his horn, emmiting a coninuous sound at a frequency of 10 rads/sec. The second rider waits just the right amount of time before also blasting his horn, so that the two sound waves are exactly π/6 radians out of phase (you can take the speed of sound in air to be v = 343 m/s, and the density of air to be 1.2 kg/m3).
a) If the sound level of each horn is 100 dB, what is the intensity of the total sound from the two horns? Express your answer as a numerical value in units W/m2.
b) If the light turns green and the bike then speeds off at 100 m/s with the horns still blaring, what apparent frequency is heard by a person left standing by the intersection?
Sound level=10log (I/(10^/12))
The Attempt at a Solution
To start, I figure I have to calculate the intensity of each horn and, if I use the equation above, it comes out to I=10^-2 w/m^2. Because the horns are out of phase by π/6 but have the same frequency, I know that complex wave is created, so I don't think the intensity would just double. How do I calculate the difference in intensity resulting from the phase change?