On your way to see your favorite band perform, you hear a solitary note being pl

Question

On your way to see your favorite band perform, you hear a solitary note being played over the loudspeaker at the concert venue. The sound is loud enough that you can hear it in your car several miles (4 miles, to be exact) from the concert. Looking at your speedometer, you notice that you are moving at a steady 15 m/s. Sitting in the back seat, you pull out your pitch pipe and it shows that the note you hear has a frequency of
457 Hz. (Sound velocity in air = 343 m/s).
A. What is the actual frequency being played?

B. You pull out your sound meter (the same ones used in the NBA playoffs to show how loud an arena is) and it registers 65 dB. After a few minutes, you see a sign that says "Concert

Explanation / Answer

Part A)

Apply the Doppler Effect

f' = f(v - vs)/v

457 = f(343 - 15)/343

f = 477.9 Hz (Round to 478 Hz)

Part B)
Apply B = 10logI/Io

65 = 10log(I/1 X 10-12)

I = 3.16 X 10-6 W/m2

4 miles is 6437.38 meters

P = IA = (3.16 X 10-6)(4pi)(6437.38)2

P = 1646.75 Watts

New intensity at 2 miles where 2 miles is 3218.69 meters

I = P/A = (1646.75)/4pi(3218.69)2

I = 1.265 X 10-5 W/m2

New decibel level

B = 10log(1.265 X 10-5)/(1 X 10-12)

B = 71.0 dB

Part C)
Apply the Doppler effect

80 mph is 35.76 m/s

60 mph = 26.82 m/s

f' = f(v + vs)/(v + vo)

f'/f = (343 + 35.76)/(343 + 26.82)

f'/f = 1.024

Thus the increase is 2.4%

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

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