Question

A factory whistle blows at a frequency of 1216 HZ. What pitch will the passengers of a car moving at 28 m/s away from the whistle hear if the speed of sound is 343 m/s.1) 1315 Hz2) 1324 Hz3) 1188 Hz4) 1117 Hz

Answer 1

Given,

The frequency of the source, f=1216 Hz

The speed with which the car is moving away from the source, v₀=28 m/s

The speed of the sound, v=343 m/s

The frequency with which the observer hears the sound is given by,

$f_0=\frac{v-v_0}{v}f$

On substituting the known values,

$\begin{gathered} f_0=\frac{343-28}{343}\times1216 \\ =1116.7\text{ Hz} \\ \approx1117\text{ Hz} \end{gathered}$

Thus the frequency heard by the observer is 1117 Hz. Therefore the correct answer is option 4.