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Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A signal source starts from rest and moves away from a stationary wall with an acceleration of $0.5 m/s^2$. After what time in secs will we hear an echo

  1. $1.2 $
  2. $8.2 $
  3. $18.2 $
  4. $4.2 $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Distance required for an echo to be heard is 17 m. Thus, $17 =  0 + \dfrac{0.5 t^2}{2} \implies t= 2\sqrt{17}=8.2 s$. 

The correct option is (b)

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A source of sound is kept at a distance of 10 m from a wall. What distance should it be moved further, so that an echo is heard

  1. 10 m away from the wall

  2. 7 m away from the wall

  3. 7 m towards the wall

  4. 10 m towards the wall
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

To hear an echo, the distance between the source and the reflector should be atleast 17 m. Thus the source should be moved 7 m away from the wall

The correct option is (b)

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A source of sound moves with an uniform velocity away from a wall. An echo is heard at 4th second from its beginning position, what is the speed of the source

  1. 10 m/s

  2. 7 m/s

  3. 4.25 m/s

  4. 1 m/s
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

distance moved by the source = 17 m for the echo to be heard

Thus, $17 = v(4) \implies v = 17/4 = 4.25 $ m/s

The correct option is (c)

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

The minimum distance between the sound and the reflecting surface, in order to hear an echo, must be

  1. $0.65\space m$
  2. $1.65\space m$
  3. $16.5\space m$
  4. $165\space m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the distance between the source of sound and the obstacle be $x$ metres .

Thus the distance travelled by sound to reach back to the source   $d = 2  x$
As the minimum time required to hear an echo is equal to $ 0.1  sec$
As velocity of sound in air    $ v = 330   m/s$
Thus  $d = v  t$
$2  x = 330  \times 0.1             \implies x = 16.5   m$

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

Velocity of sound in the atmosphere of a planet is 600m$s^{-1}$. The minimum distance between the source of sound and the obstacle to hear echo should be

  1. 60 m

  2. 25 m

  3. 30 m

  4. 17 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the distance between the source of sound and the obstacle be $x$ metres .

Thus the distance travelled by sound to reach back to the source   $d = 2  x$
As the minimum time required to hear an echo is equal to $ 0.1  sec$
Thus  $d = v  t$
$2  x = 600  \times 0.1             \implies x = 30   m$

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A source of sound emitting a tone of frequency 200 Hz moves towards an observer with a velocity v equal to the velocity of sound if the observer also moves away from the source with the same velocity v, the apparent frequency heard by the observer is

  1. $50 Hz$
  2. $100 Hz$
  3. $150 Hz$
  4. $200 Hz$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to the Doppler effect, if both the source and observer move at the same velocity in the same direction, the relative velocity between them is zero. Therefore, the frequency heard remains the same as the source frequency.

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A table is revolving on its axis at 5 revolutions per second. A sound source of frequency 1000 Hz is fixed on the table at 70 cm from the axis. The minimum frequency heard by a listener standing at a distance from the table will be (speed of sound = 352 m/s)

  1. 1000 Hz

  2. 1066 Hz

  3. 941 Hz

  4. 352 Hz
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\begin{array}{l} For\, \, source\, \, vS=r\omega =0.70\times 2\pi \times 5=22\, m/s \ the\, \, source\, \, is\, \, receding\, \, the\, \, man.\, it\, \, is\, \, given\, \, by\, \, { \eta _{ \min   } }=n\frac { v }{ { v+{ v _{ s } } } } Hz \ Minimum\, \, frequency\, \, is\, \, heard\, \, when=1000\times \frac { { 352 } }{ { 352+22 } } =941 \end{array}$

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A person clapped his hands hear cliff and heard a echo after 5s. The minimum distance of the cliff from the person if the speed of sound is take as 346 m/s 

  1. 17.11 m

  2. 117.2 m

  3. 173 m

  4. 865 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The total distance traveled by the sound is speed times time: 346 m/s * 5 s = 1730 m. Since the sound travels to the cliff and back, the distance to the cliff is half of the total distance: 1730 / 2 = 865 m.

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

A mas fires a bullet standing between two cliffs. First echo is heard after $3$ seconds and second echo is heard after $5$ seconds. If the velocity of sound is $336m/s$, then the distance between the cliffs is

  1. $5\times 336 m$
  2. $4\times 336 m$
  3. $3\times 336 m$
  4. $2\times 336 m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The distance to the first cliff is d1 = (v * t1) / 2 and the second is d2 = (v * t2) / 2. The total distance between the cliffs is d1 + d2 = (v/2) * (t1 + t2) = (336/2) * (3 + 5) = 168 * 8 = 1344 m. This equals 4 * 336 m.