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Homework Help: Sound wave propblem

  1. Jul 21, 2010 #1
    1. The problem statement, all variables and given/known data
    The speed of the sound in the air (in meter per second) depends on temperature according to approximate expression
    V= 313.5 + 0.607Tc
    where Tc is the Celsius temperature. In dry air, the temperature decreases about 1 degree Celsius for every 150M rise in altitude

    2. Relevant equations
    a) assume the change is constant up to an altitude of 9000m what time interval is required for the sound from airplane flying at 9000m to reach the ground on a day when the ground temperature is 30 Celsius
     
  2. jcsd
  3. Jul 21, 2010 #2
    Please show some work.
     
  4. Jul 21, 2010 #3
    I have tried to make integration because the velocity is changing
    I said that T =[tex]\frac{x}{v}[/tex] >>
    x = 9000 m
    v = [tex]\int(313.5+0.607t)dt[/tex] and the limit of integration fro, -30 to 30
    but it doesn't work
     
  5. Jul 21, 2010 #4
    I'm not sure what you mean by dv=vdt (deduced from your integral). Anyway, here is the way:
    1 - We have dt = dx/v
    2 - As v is given depending on T (note: t and T are different, one is time, the other is temperature), and we also have the variation law of T versus x (x is also height), we can derive v versus x.
    Then, it's just simple math :wink:
     
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