JEE Mains · Physics · STD 11 - 14. waves and sound
A train is moving on a straight track with speed \(20\ ms^{-1}\). It is blowing its whistle at the frequency of \(1000\ Hz\). The percentage change in the frequency heard by a person standing near the track as the train passes him is ( speed of sound \(=320\) \(ms^{-1}\) ) close to .... \(\%\)
- A \(12\)
- B \(18\)
- C \(24\)
- D \(6\)
Answer & Solution
Correct Answer
(A) \(12\)
Step-by-step Solution
Detailed explanation
\(f_{1}=f\left[\frac{v}{v-v_{s}}\right]=f \times \frac{320}{300} \mathrm{Hz}\) \(f_{2}=f\left[\frac{v}{v+v_{s}}\right]=f \times \frac{320}{340} \mathrm{Hz}\) \(\left(\frac{f_{2}}{f_{1}}-1\right) \times 100=\left(\frac{300}{340}-1\right) \times 100 \simeq 12 \%\)
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