I drive in my car at v_L= 18 m/s down a road. Two motorcycles are also driving d

Question

I drive in my car at v_L= 18 m/s down a road. Two motorcycles are also driving down the road, both at 20 m/s. When one motorcycle is ahead of me, and one behind, I hear a beat frequency. The motorcycles engines both produce a frequency of 400 Hz. The speed of sound is 344 m/s. What frequency do I hear from the motorcycle behind me? What frequency do I hear from the motorcycle ahead of me? What beat frequency do I hear? When a motorcycle is 3 m away, the intensity of the sound from the engine is 0.6 W/m^2. What is the sound intensity level (in decibels) of a single motorcycle engine at 3 m? If both motorcycles are 3 m away, what is the sound intensity level (in decibels) of sound from both of their engines combined?

Explanation / Answer

A)the frequency heared me by behind motor cycle n1=n (V-V0/V-VS)

n1=400(344-18/344-20)=402 hz

B

the frequency heared me by ahead motor cycle n1=n (V+V0/V+VS)

n1=400(344+18/344+20)=397 hz

c)beat frequency =402-397=5

d)sound intensity level from one motor cycle IL=10 log10I/I0

here I0=10-12w/m2,I=6*10-1w/m2

IL=10 log 106*10-1/10-12=85.59 db

e)sound intensity level from two motor cycle IL=10 log10I/I0

here I0=10-12w/m2,I=12*10-1w/m2

IL=10 log 1012*10-1/10-12=118.70 db

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