JEE Advanced · Physics · 16. Waves & Sound
Paragraph:
Two trains \(A\) and \(B\) are moving with speeds \(20 \mathrm{~m} / \mathrm{s}\) and \(30 \mathrm{~m} / \mathrm{s}\), respectively in the same direction on the same straight track, with \(B\) ahead of \(A\). The engines are at the front ends. The engine of train \(A\) blows a long whistle.
Assume that the sound of the whistle is composed of components varying in frequency from \(f_1=800 \mathrm{~Hz}\) to \(f_2=1120 \mathrm{~Hz}\), as shown in the figure. The spread in the frequency (highest frequency - lowest frequency) is thus \(320 \mathrm{~Hz}\). The speed of sound in still air is \(340 \mathrm{~m} / \mathrm{s}\).
Question:
The speed of sound of the whistle is
- A \(340 \mathrm{~m} / \mathrm{s}\) for passengers in \(A\) and \(310 \mathrm{~m} / \mathrm{s}\) for passengers in \(B\)
- B \(360 \mathrm{~m} / \mathrm{s}\) for passengers in \(A\) and \(310 \mathrm{~m} / \mathrm{s}\) for passengers in \(B\)
- C \(310 \mathrm{~m} / \mathrm{s}\) for passengers in \(A\) and \(360 \mathrm{~m} / \mathrm{s}\) for passengers in \(B\)
- D \(340 \mathrm{~m} / \mathrm{s}\) for passengers in both the trains
Answer & Solution
Correct Answer
(B) \(360 \mathrm{~m} / \mathrm{s}\) for passengers in \(A\) and \(310 \mathrm{~m} / \mathrm{s}\) for passengers in \(B\)
Step-by-step Solution
Detailed explanation
\(v_{S A}=340+20=360 \mathrm{~m} / \mathrm{s}\) \(v_{S B}=340-30=310 \mathrm{~m} / \mathrm{s}\)
Therefore, correct option is (b).
Therefore, correct option is (b).
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