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

Question

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with speed of

20m{s}^{- 1}

with respect to the ground. If an observer in car A detects a frequency

2000Hz

of the sound coming from car B, what is the natural frequency of the sound source in car B?
(speed of sound in air

= 340m{s}^{- 1}

)

Quantrex Academy · Accepted Answer

Correct answer: C. 2250Hz

From Doppler effect: f' = ( V ∓ V _ 0 V ± V _ S ) f _ 0 2000 = ((340 - 20)/(340 + 20)) f _ 0 = ((320)/(360)) f _ 0 f _ 0 = (9)/(8) × 2000 = 2250Hz

Two cars A and B are moving away from each other in opposite...