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Homework Help: Pain Threshold - Reducing Intensity

  1. Jan 20, 2010 #1
    1. The problem statement, all variables and given/known data

    At a distance of 30 m the noise from the engine of an jet has an intensity of 130 dB.

    At this level, you will be in pain and your ears will hurt. That's why this intensity is know as the "pain threshold".

    How far do you have to be from a jet (total distance), in order for the noise to drop down in intensity to 62.2 dB, a level comparable to that of a spoken conversation?

    Express the result in the unit m, and to three significant figures.

    2. Relevant equations

    I think Intensity is proportional to (1/r^2)

    I = (dE/dt) / 4pi(r^2)

    I=1/2v(w^2)(A^2) where w = the angular frequency and A - the amplitude

    3. The attempt at a solution

    I am not sure how to manipulate the equations
  2. jcsd
  3. Jan 22, 2010 #2
    PLease help

    I was trying the formula I2/I1 = A1/A2 = 4pi(r1^2)/ 4pi(r2^2)

    I got 30.4 which is wrong
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