Question

A car sounding its horn at 480 Hz moves towards a high wall at speed of 20m/s , the frequency of reflected sound heard by man sitting in car will be nearest to

Answer 1

from Doppler's effect of sound, After reflection from the wall, the sound moves towards observer in the car, frequency is given as $f=f_0\left(\frac{v+v_0}{v-v_s}\right)$

here, $f_0$ is the frequency of sound of car's horn.

$v_0$ is the speed of observer

$v_s$ is the speed of source.

and v is speed of sound.

here, $f_0$ = 480Hz , $v_0$ = 20m/s, $v_s$ = 20m/s and v = 340m/s [ speed of sound ]

so, f = 480 × (340 + 20)/(340 - 20)

= 480 × 360/320

= 540 Hz

hence, frequency of reflected sound heard by man sitting in car will be 540 Hz.