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Homework Help: Sound waves

  1. Feb 26, 2010 #1
    1. The Young's modulus for tin is 4.5x10^10. If the speed of sound in tin is measured to be 2.73km/s , find its density in (kg/m^3) .

    a)6.05x10^3
    b)23.8x10^3
    c)6.35x10^3
    d)24.5x10^3
    e)6.65x10^3

    , E(tin)=4.5x10^10 ,speed of sound in tin=2.73km/s




    2. v=sqrt(B/density) -where B is bulk modulus



    3. if i substitute B as young's modulus I get answer a) in the choices.


    What is difference between bulk modulus and young's modulus and if there is what relation relates them.Thanks.
     
  2. jcsd
  3. Feb 26, 2010 #2

    rl.bhat

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    Bulk modulus = 3*young's modulus.
     
  4. Feb 26, 2010 #3
    But when i substitute v=sqrt(3Y/density)=sqrt(B/density) i dont get an answer from choices while i do if i substitute v=y/density.is it possible that in sound waves the velocity is proportional to youngs modulus instead of bulk modulus as in other cases.


    From serway :"For longitudinal sound waves in a solid rod of material, for example, the speed of
    sound depends on Young’s modulus Y and the density !. Table 17.1 provides the speed
    of sound in several different materials"

    please advise.:)
     
  5. Mar 1, 2010 #4
    any idea anybody?:confused:
     
  6. Mar 1, 2010 #5

    rl.bhat

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    While calculating the velocity of sound in solid, if the solid is a thin rod, the bulk modulus is replaced by Young's modulus.
     
  7. Mar 1, 2010 #6
    thanks very much.
     
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