I drive my car at VL= 18m/s down a road. Two motorcycles are also driving down t

Question

I drive my car at VL= 18m/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 me, I hear a beat frequency. The motorcycles' engines both produce a frequency of 400 Hz. The speed of sound is 344 m/s. When a motorcycle is 3m away, the intensity of the sound from the engine is 0.6W/m^2.

1. What is the sound intensity level (in decibels) of a single motorcycle engine at 3m.

2. If both motorcycles are 3m away, what is the sound intensity level (in decibels) of the sound from both of their engines combined?

Explanation / Answer

f = (c+Vr)fo/(c+vs)
a) f = (344+18)400/(344-20) = 446.91 Hz
b) f = (344+18)400/(344+20) = 397.80 Hz
c) fbeat = f1-f2 = 49.107 Hz
d) I = 10*log(0.6/10^-9) = 87.781 db

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.