I drive in my car at V_L=18 m/s down a road. The motorcycles are also driving do
ID: 1517605 • Letter: I
Question
I drive in my car at V_L=18 m/s down a road. The 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 the sound from both of their engines combined?Explanation / Answer
a) frequency from behind motorcycle = [(344 - 18)/(344 - 20)] * 400
= 402.469 Hz
b) frequency from ahead motorcycle = [(344 + 18)/(344 + 20)] * 400
= 397.802 Hz
c) Beat frequency = f1 - f2
= 402.469 - 397.802 = 4.667 Hz
d) sound intensity level = 10 * log(0.6/10-12)
= 117.78 dB
e) sound intensity level for both motorcycles = 10 * log(1.2/10-12)
= 120.79 dB
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.