A stationary source is emitting sound at a fixed frequency f_0, w… - Vidyadip

MCQ

A stationary source is emitting sound at a fixed frequency $\mathrm{f}_0$, which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is $1.2 \%$ of $f_0$. What is the difference in the speeds of the cars (in $\mathrm{km}$ per hour) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound which is $330 \mathrm{~ms}^{-1}$.

✓
$7$
B
$9$
C
$3$
D
$5$

✓

Answer

Correct option: A.

$7$

a
$f_{\text {app }}=f_0 \frac{c+v}{c-v}$

$\mathrm{df}=\frac{2 \mathrm{f}_0 \mathrm{c}}{(\mathrm{c}-\mathrm{v})^2} \mathrm{dv}$

where $c$ is speed of sound

$\mathrm{df}=\frac{1.2}{100} \mathrm{f}_0$

hence $d v \approx 7 \mathrm{~km} / \mathrm{hr}$.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

JEE STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

Match list - i with list - ii.

LIST – I	LIST - II
(A) Permeability of free space	(I) $\left[ M L ^2 T^{-2}\right]$
(B) Magnetic field	(II) $\left[ M T ^{-2} A^{-1}\right]$
(C) Magnetic moment	(III) $\left[ M L T ^{-2} A^{-2}\right]$
(D) Torsional constant	(IV) $\left[ L ^2 A\right]$

An elevator weighing $6000\, kg$ is pulled upward by a cable with an acceleration of $5\,m{s^{ - 2}}$. Taking g to be $10\,m{s^{ - 2}}$, then the tension in the cable is ........... $N$

The speed of a wave in a medium is $760\, m/s$. If $3600 $ waves are passing through a point, in the medium in $2$ minutes, then its wavelength is ...... $m$

The fundamental frequency of a sonometer wire is increases by $6\, Hz$ if its tension is increased by $44\%$, keeping the length constant. The frequency of the wire is ...... $Hz$

The circuit diagram shown here corresponds to the logic gate,

$Assertion$ : In a free fall, weight of a body becomes effectively zero.
$Reason$ : Acceleration due to gravity acting on a body having free fall is zero.

Parallel beam of light is incident on a system of two convex lenses of focal lengths $f_1 = 20\, cm$ and $f_2 = 10\, cm$. What should be the distance between the two lenses so that rays after refraction from both the lenses pass undeviated :........$cm$

A round body is given translational velocity and released on a surface that has friction. Then

At standard temperature and pressure the density of a gas is $1.3$ $kg/{m^3}$ and the speed of the sound in gas is $330\, m/sec.$ Then the degree of freedom of the gas will be

In which of the following stores maximum energy ?