Problem 4.13: Sound waves travel through air at a speed of 330 m/s. A whistle blast at a frequency of about 1.0 kHz lasts for 2.0 s. (a) Over what distance in space does the "wave train" representing the sound extend? (b) What is the wavelength of the sound? (c) Estimate the precision with which an observer could measure the wavelength. (d) Estimate the precision with which an observer could measure the frequency.

a)  x = 660 m, b)  λ = 0.330 m, c) Δλ = 0.1 cm, d)    Δf = 104

Explanation:

a) the distance in which the train of waves extends can be obtained from the uniform movement

             v = x / t

             x = v t

             x = 330 2

             x = 660 m

b) the speed of sound is related to the wavelength and frequency

             v = λ f

              λ = v / f

              λ = 330/1000

              λ = 0.330 m

c) The precision in the measurement of the wavelength refers to the error or uncertainty in the measurement, if the measurement is direct with a tape measure the precision is the appreciation of the tape measure, in general it is 0.1 cm

d) the accuracy of the frequency in general the frequency is calculated from the measurements of period T

                f = 1 / T

The precision of the period is data by the chronometer used, in general time a press of 0.01s, by the response time of the people

               Δf = df / dT    ΔT

               Δf = 1 / T² ΔT

                Δf = 1 / (0.001)² 0.01

                 Δf = 104

As we can see, a much more precise system is needed to reduce the error

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