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Need help on EM waves problem

  1. Mar 26, 2007 #1
    1. The problem statement, all variables and given/known data
    An important news announcement is transmitted by radio waves to people who are 81 km away, sitting next to their radios, and by sound waves to people sitting across the newsroom, 2.3 m from the newscaster. Take the speed of sound in air to be 343 m/s. What is the difference in time that the message is recieved?

    2. Relevant equations
    c = f*lamda

    3. The attempt at a solution
    c1 = 3*10^8 m/s
    lamda1 = 81km
    c2 = 343 m/s
    lamda2 = 2.3m

    f1 = c1/lamda1
    f2 = c2/lamda2

    T = 1/(f1-f2) = time difference

    What am I doing wrong? Thanks in advance for any help!
  2. jcsd
  3. Mar 26, 2007 #2
    I think this is more of a distance problem than a waves problem.

    So, the speed of radio waves is the speed of light, 3*10^8 m/s....so use time=distance/speed
    Do the same thing for sound, where it travels at 343 m/s.
  4. Mar 26, 2007 #3
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