Question

A train running at 108 km $h^{-1}$ towards east whistles at a dominant frequency of 600 Hz. Speed of sound in air is 340 m/s. What frequency will a passenger sitting near the open window hear ? (b) What frequency will a person standing near the track hear whom the train has just passed ? (c) A wind starts blowing towards east at a speed of 36 km $h^{-1}$. Calculate the frequencies heard by the passenger in the train and by the person standing near the track.

Answer 1

(a)Velocity of passenger with respect to the train is zero. So, Required frequecny =500 Hz

(b)Frequency heard by the person standing near the track,

$n=\frac{v+v_0}{v+v_s}\times n_0$

$=\frac{340+0}{340+30}\times 500=459Hz$

(c)When the wind starts blowing towards east.

Frequency heard by passenger is unaffected.

But frequency heard by passenger is unaffected.

But frequency heard by person stadly near the track,

$n=\frac{(v-v_{air})}{(v-v_{air})+v_s}\times n_0$

$=\frac{(340-10)}{(340-10)+30}\times 500$

=458 Hz