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Homework Help: Speed of sound problem

  1. Feb 8, 2016 #1
    I have a question to solve - A boy heard a sound of frequency 100 Hz at a distance of 500 m from the source of sound. What is the speed of sound? What is the time period of oscillating particles of the medium?

    I have approached the below way :

    We know that speed = distance / time [1/T=Frequency)

    Hence speed = distance x Frequency = 500 m x 100 Hz = 50 km

    Now given that Frequency is 100 Hz which is nothing but 100 oscillation per sec = So 1 oscillation = 1 / 100 = 0.01 sec.

    Please let me know if my answers are correct?
  2. jcsd
  3. Feb 8, 2016 #2


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    Gold Member

    There is not enough information here to answer anything. This does not seem to be a meaningful question.
  4. Feb 8, 2016 #3
    Thanks - can you please explain me what information is missing - is my calculation to calculate the speed of sound is correct as mentioned in my main post?
  5. Feb 8, 2016 #4


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    Homework Helper

    No. You gave the speed as "50 km", which has units of distance. Speed has units of distance per unit time.

    You can look up the speed of sound in air to see what an accurate answer might be.
  6. Feb 8, 2016 #5


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    You are misusing the formulae : speed = distance / time and 1/T=Frequency
    Here T is not the general quantity "time" , but specifically the time for one cycle of the sound
    Your conclusion, "Hence speed = distance x Frequency" would be true only when time was the duration of one cycle and distance was one wavelength.
    The correct conclusion is that speed = wavelength x frequency ( = distance traveled by the sound during one cycle x frequency)
    or that speed = distance traveled by the sound during one cycle / duration of one cycle (= wavelength / T )
  7. Feb 8, 2016 #6
    Thanks - I got your point - thanks for the lucid explanation and clearing my concept
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