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JEE Advanced 2007Paper 2

Exam: JEE Advanced
Year: 2007
Paper: Paper 2
Subject: Physics
Chapter: Waves and Sound

JEE Advanced 2007 · Paper 2 · Physics · Waves and Sound

Paragraph: Two trains A and B are moving with speeds 20 ~m / s and...

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

Options

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

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

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).

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