A pair of die-hard sports fans decide to ride their motorcycle to the local game

ID: 2275627 • Letter: A

Question

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 pi/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 o at 100 m/s with the horns still blaring,

what apparent frequency is heard by a person left standing by the intersection?

a)sqrt(100^2+100^-2*100*100*cos(pi/3))=100 dB

b)velocity of source=vs=100 m/s away from receiver

velocity of receiver=vr=0

velocity of sound=v=343 m/s

so frequency heard=10*(343+0)/(343+100)=7.7426 rad/sec

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