JEE Main 2021PhysicsWaves and SoundMediumNumerical

JEE Main 2021 — Waves and Sound Question with Solution

JEE Main 2021 (20 Jul Shift 1)

Question

The frequency of a car horn encountered a change from 400 Hz to 500 Hz. When the car approaches a vertical wall. If the speed of sound is 330 m s-1. Then the speed of car is ___ km h-1.

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Show full solutionCorrect answer: 132
Correct answer
132

Step-by-step explanation

Wall as an observer
Frequency received by wall, 

f1=f0CC-V
Again wall as a source
Frequency received by observer on car, 
f2=f1C+VC
f2=f0C+VC-V
500=400C+VC-V
54=C+VC-V
C=9 V

V=C9=3309 m s-1
V=3309×185=132 km h-1

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About this question

This is a previous-year question from JEE Main 2021, covering the Waves and Sound chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.