Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 ms-1 with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency (in Hz) of the sound source in car B? (speed of sound in air =340 ms-1)

Question

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 ms-1 with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency (in Hz) of the sound source in car B? (speed of sound in air =340 ms-1) (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

f ' =f (v-v0/v+vs) or 2000 = f (340-20/340+20) ∴ f = 2250 Hz

f′=fv+vs​v−v0​​ or 2000=f340+20340−20​ ∴f=2250Hz

$f^{'} = f \frac{v - v _{0}}{v + v _{s}}$
or $2000 = f \frac{340 - 20}{340 + 20}$
$∴ f = 2250 Hz$