Tag: determination of speed of sound by echo

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Questions Related to determination of speed of sound by echo

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

If d is the distance between the source of sound and reflector $t _1, t _2$ are times at which echoes are heard, the expression for determination of velocity of sound in air by echo method is :

  1. $\displaystyle \frac{2d}{t _2-t _1}$

  2. $\displaystyle \frac{2d}{t _1-t _2}$

  3. $\displaystyle \frac{4d}{t _1-t _2}$

  4. $\displaystyle \frac{2d}{t _1+t _2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The speed of the sound, distance traveled and the time taken relationship if the sound is a reflected sound, that is echo, it is given as follows.
$Speed\; of \; sound=\dfrac { 2\times Distance\; traveled\; (m) }{ Time\; taken(s) } $.
In the question it is given that distance traveled by the sound from the source to the reflector is d and the time taken to hear the echo are $t _1$ and $t _2$ seconds.
The speed of the sound wave is calculated as follows.$v=\dfrac { 2d }{ t _1-t _2 } m/s$.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A man stands at a distance of $225 m$ from a cliff. He fires a gun and heard the echo after $1.5 sec$. What will be the velocity of the sound?

  1. ${ 300ms }^{ -1 }$

  2. ${ 340ms }^{ -1 }$

  3. ${ 320 ms }^{ -1 }$

  4. ${ 335 ms }^{ -1 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The echo is the sound reflection from a surface. Thus, total distance be covered by sound is $d=2\times 225=450 m$.

Using , $S=vt$, we get $v=d/t=450/1.5=300 m/s$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

An echo returns in 30 s. What is the distance of the reflecting surface from the source? 

Given that speed of sound= 342m/s

  1. 5100 m

  2. 22.66m

  3. 5130 m

  4. 22.8 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Time taken by the wave to travel from the sound to the reflecting surface $= t = \dfrac{30}{2} = 15 m$
Speed $= 342 m/s$ 
Distance of reflecting surface from the sound $= 342 \times 15 = 5130 m$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A man standing in front of a large wall claps at a regular frequency of $10Hz$. He finds that the echoes coincide with his clapping. (The speed od sound in air is $330ms^{-1}.)$
(i) Time taken between successive clapping is $0.1s$.
(ii) The distance between the man and the wall, after he clapping, If he hears one more echo is $33m$.
(iii) The distance between the man and the wall, after he stops clapping, if he hears four more echoes is $66m$.

  1. Only (i) and (ii) are correct.

  2. Only (ii) and (iii) re correct.

  3. Only (i) and (iii) are correct.

  4. All (i), (ii) and (iii) are correct.
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A boy clapped his hands near a cliff and heard the echo after 4s. What is the distance of the cliff from the person if the speed of the sound, v is taken as 346 ms$^{-1}$?

  1. 2 m

  2. 1384 m

  3. 692 m

  4. 2768 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given, Speed of sound, $v = 346 ms^{-1}$ Time taken for hearing the echo, $t = 4 s$
Distance travelled by the sound $ = v \times t = 346 m/s \times 4 s = 1384 m$
In 4 s sound has to travel twice the distance between the cliff and the person.
Hence, the distance between the cliff and the person $= 1384 m/2 = 692 m$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A sound wave of wavelength $\lambda$ travels towards the right horizontally with a velocity V. It strikes and reflects from a vertical plane surface, travelling at a speed v towards the left. The number of positive crests striking during a time interval of three seconds on the wall is :

  1. $3(V+v)/\lambda$

  2. $3(V-v)/\lambda$

  3. $(V+v)/3\lambda$

  4. $(V-v)/3\lambda$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The relative velocity of the wave crests with respect to the wall is (V+v). The distance covered by the crests in time t is (V+v)t. The number of crests is distance / wavelength = (V+v)t / lambda. For t=3s, this is 3(V+v)/lambda.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A person is in front of a fort wall.  The person can hear an echo of sound produced by him when minimum distance between person and wall is 16.75 m. The velocity of sound in air is:

  1. 330 m/s

  2. 335 m/s

  3. 337.5 m/s

  4. 345 m/s
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Minimum time for echo is $0.15$
So, distance travelled for echo is $=2\times 16.75=$ speed of sound $\times$ minimum time for echo
$\Rightarrow 2\times 16.75=\vartheta _{s}\times 0.1$

$\Rightarrow \vartheta _{s}=\dfrac{2\times 16.75}{0.1}$$=335 m/s$