50fg per correct answer

1) You are at a rock concert, and the sound intensity reaches levels as high as 100 dB. The sound pressure produces an oscillating force on your eardrum.area of ear drum is 50 mm^2
Calculate the amplitude of this oscillating force.


2) A person has severe hearing loss that reduces the intensity in his inner ear by 28.8 dB. To compensate, a hearing aid can amplify the sound pressure amplitude by a certain factor to bring the intensity level back to the value for a healthy ear. What amplification factor is needed for this person?


3) A siren has a frequency of 849 Hz when it and an observer are both at rest. The observer then starts to move and finds that the frequency he hears is 1256 Hz observer is moving toward the siren.
What is the speed of the observer?

2. 758.5775

3)

f' = (v+vo)/v*f
Assume speed of sound is 343.2 m/s
1256 = (343.2+vo)/343.2*849
vo = 164.5 m/s <- velocity of observer toward stationary source



3dB = double
28.8/3 = 9.6
2^9.6 = 776.05

Somewhere in that vicinity.

This post was edited by Dontrunaway on Dec 9 2013 06:55pm

1e-4 N for 1

1.99526....^9.6= 758.577

sent fg to above

although 2 is coming up wrong

Sound intensity level (energy quantity) LI = 28.8 dB
Energy amplification factor (acoustic intensity) x = 10^(LI/10) = 10^(28.8/10) = 10^2.88 = 758.578 should be right for 2? o.O

oo, ok
I see I've misread the question

answer is 4.22079