Physics · Sound Waves

JEE Advanced 2019 — Paper 1 — Question 14

A train S1, moving with a uniform velocity of 108 $\mathrm{km} / \mathrm{h}$ , approaches another train S2 standing on a platform. An observer O moves with a uniform velocity of $36 \mathrm{~km} / \mathrm{h}$ towards S 2 , as shown in figure. Both the trains are blowing whistles of same frequency 120 Hz . When O is 600 m away from S2 and distance between S 1 and S 2 is 800 m , the number of beats heard by O is $\_\_\_\_$ . [Speed of the sound $=330 \mathrm{~m} / \mathrm{s}$ ]

Answer: 8.13

Numerical answer — enter this value.

Step-by-step solution

$f_{1}=120\left(\frac{330+10 \cos 53}{330-30 \cos 37^{\circ}}\right)$

$\mathrm{f}_{2}=120\left(\frac{330+10}{330}\right)$

$\mathrm{f}_{\mathrm{b}}=\left|\mathrm{f}_{1}-\mathrm{f}_{2}\right|=8.128 \mathrm{~Hz}=8.13 \mathrm{~Hz}$

Answer key and solution verified before publishing.

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Exam: JEE Advanced 2019
Paper: Paper 1
Subject: Physics
Chapter: Sound Waves
Topic: Doppler Effect of Sound