Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app

JEE Main 201511 AprilOnline

Exam: JEE Main
Year: 2015
Date: 11 April
Mode: Online
Subject: Physics
Chapter: Waves and Sound

JEE Main 2015 · 11 April · Online · Physics · Waves and Sound

A source of sound emits sound waves at frequency f _ 0 . It is...

A source of sound emits sound waves at frequency ${f}_{0}$ . It is moving towards an observer with fixed speed ${v}_{s} ( {v}_{s} < v)$ , where $v$ is the speed of sound in air). If the observer were to move towards the source with speed ${v}_{0}$ , one of the following two graphs (A and B) will give the correct variation of the frequency $f$ heard by the observer as ${v}_{0}$ is changed.

A source of sound emits sound waves at frequency f _ 0 . It is moving towards an observer with fixed speed v _ s ( v _

The variation of $f$ with ${v}_{0}$ is given correctly by:

Options

AGraph A with slope $= \dfrac{{f}_{0}}{\left(v - {v}_{s}\right)}
BGraph A with slope $= \dfrac{{f}_{0}}{\left(v + {v}_{s}\right)}
CGraph B with slope $= \dfrac{{f}_{0}}{\left(v - {v}_{s}\right)}
DGraph B with slope $= \dfrac{{f}_{0}}{\left(v + {v}_{s}\right)}

Correct answer

A. Graph A with slope $= \dfrac{{f}_{0}}{\left(v - {v}_{s}\right)}

Step-by-step solution

A source of sound emits sound waves at frequency f _ 0 . It is moving towards an observer with fixed speed v _ s ( v _

{f}_{app} = \dfrac{v + {v}_{0}}{v - {v}_{s}}{f}_{0}

⇒ f = \dfrac{{f}_{0}}{v - {v}_{s}}{v}_{0} + \dfrac{v{f}_{0}}{v - {v}_{s}}

On comparing with

y = mx + c

m = \dfrac{{f}_{0}}{v - {v}_{s}}

and

c = \dfrac{v{f}_{0}}{v - {v}_{s}}

⇒

Graph with +ve slope and +ve intercept.

Practice Waves and Sound on Quantrex Academy →

More from Waves and Sound

List-I shows four configurations made of straight and semi-circular narrow tubes… JEE Advanced 2026 A transverse wave on a string is described by y = 3 (36t + 0.018x + π/4) , where x, y are… JEE Main 2026 The equation of a plane progressive wave is given by y = 5 π(200t - (x)/(150)) where x… JEE Main 2026 The speed of a longitudinal wave in a metallic bar is 400 ~m / s . If the density and… JEE Main 2026 Two tuning forks A and B are sounded together giving rise to 8 beats in 2 s. When fork A… JEE Main 2026 A point source is kept at the center of a spherically enclosed detector. If the volume of… JEE Main 2026 The fifth harmonic of a closed organ pipe is found to be in unison with the first… JEE Main 2026 The velocity of sound in air is doubled when the temperature is raised from 0^ ∘ C to α^… JEE Main 2026 Full Waves and Sound list All JEE Main PYQs