Download App

14. waves and sound — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A source of sound is travelling towards a stationary observer. The frequency of sound heard by the observer is of three times the original frequency. The velocity of sound is $v\, m/sec.$ The speed of source will be
  • ✓
    $\frac{2}{3}v$
  • B
    $v$
  • C
    $\frac{3}{2}v$
  • D
    $3v$
✓

Answer

Correct option: A.
$\frac{2}{3}v$
a
$n' = n\,\left( {\frac{v}{{v - {v_S}}}} \right)$

$\Rightarrow \frac{{n'}}{n} = \frac{v}{{v - {v_S}}} $

$\Rightarrow \frac{v}{{v - {v_S}}} = 3$

$\Rightarrow {v_s} = \frac{{2v}}{3}$

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

More "M.C.Q (1 Marks)" from 14. waves and sound→14. waves and sound — all question types→Physics STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

In a Carnot engine, when ${T_2} = {0^o}C$ and ${T_1} = {200^o}C,$ its efficiency is ${\eta _1}$ and when ${T_1} = 0{\,^o}C$ and ${T_2} = - 200{\,^o}C$, Its efficiency is ${\eta _2}$, then what is ${\eta _1}/{\eta _2}$
→
Two different liquids of same mass are kept in two identical vessels, which are placed in a freezer that extracts heat from them at the same rate causing each liquid to transform into a solid. The schematic figure below shows the temperature $T$ versus time $t$ plot for the two materials. We denote the specific heat in the liquid states to be $C_{L 1}$ and $C_{L 2}$ for materials 1 and 2, respectively and latent heats of fusion $U_1$ and $U_2$, respectively. Choose the correct option.
→
Two capillaries made of same material but of different radii are dipped in a liquid. The rise of liquid in one capillary is $2.2\, cm$ and that in the other is $6.6\, cm$. The ratio of their radii is
→
Two closed organ pipes of length $100\,cm$ and $101\,cm$ long give $16$ beats in $20\,sec$ when each pipe is sounded in fundamental mode. Calculate velocity of sound .... $ms^{-1}$
→
A wooden block with a coin placed on its top, floats in water as shown in the distance $l$ and $h$ are shown in the figure. After some time the coin falls into the water. Then:
→
The distance between the carbon atom and the oxygen atom in a carbon monoxide molecule is $1.1\ Å$.  Given, mass of carbon atom is $12\ a.m.u.$ and mass of oxygen atom is $16\ a.m.u.$, calculate the position of the center of mass of the carbon monoxide molecule
→
The velocity $v$ of a particle moving along $x$-axis varies with its position $(x)$ as $v=\alpha \sqrt{x}$; where $\alpha$ is a constant. Which of the following graph represents the variation of its acceleration (a) with time $(t)$ ?
→
A particle executes simple harmonic motion with an amplitude of $4 \,cm$. At the mean position the velocity of the particle is $10\, cm/s$. The distance of the particle from the mean position when its speed becomes $5 \,cm/s$ is
→
A standing wave is established in single loop. At $t = 0$ , $K.E.$  of string is zero. Choose the correct option 
→
When the temperature of a gas is $20^{\circ} C$ and pressure is changed from $P_1=1.01 \times 10^5 \,Pa$ to $P_2=1.165 \times$ $10^5 \,Pa$, then the volume changes by $10 \%$. The Bulk modulus is .........$\times 10^5 \,Pa$
→