JEE Mains · Physics · STD 11 - 14. waves and sound
Two cars \({X}\) and \({Y}\) are approaching each other with velocities \(36\; {km} / {h}\) and \(72\; {km} / {h}\) respectively. The frequency of a whistle sound as emitted by a passenger in car \({X}\), heard by the passenger in car \({Y}\) is \(1320 \;{Hz}\). If the velocity of sound in air is \(340\; {m} / {s}\), the actual frequency of the whistle sound produced is ........ \(Hz.\)
- A \(1210\)
- B \(1250\)
- C \(605\)
- D \(2420\)
Answer & Solution
Correct Answer
(A) \(1210\)
Step-by-step Solution
Detailed explanation
\({V}_{{x}}=36 {km} / {hr}=10 {m} / {s}\) \({V}_{{y}}=72 {km} / {hr}=20 {m} / {s}\) by doppler's effect \({F}^{\prime}={F}_{0}\left(\frac{{V} \pm {V}_{0}}{{V} \pm {V}_{{s}}}\right)\) \(1320={F}_{0}\left(\frac{340+20}{340-10}\right) \Rightarrow {F}_{0}=1210 {Hz}\)
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