Waves & Sound · JEE Main previous year questions

2019 12 questions

1. Q562019 · 12 Apr 2019 · Shift 1
   
   1. A.$\frac{\pi }{2}$
   2. B.$\pi$
   3. C.0
   4. D.$-\frac{\pi }{2}$
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   Answer: B

2. Q602019 · 12 Apr 2019 · Shift 1

   A submarine (A) travelling at 18 km/hr is being chased along the line of its velocity by another submarine (B) travelling at 27 km/hr. B sends a sonar signal of 500 Hz to detect A and receives a reflected sound of frequency $\upsilon$. The value of $\upsilon$ is close to: (Speed of sound in water =$1500{\text{ ms}}^{-1}$)

   1. A.507 Hz
   2. B.502 Hz
   3. C.499 Hz
   4. D.504 Hz
   Show answer

   Answer: B

3. Q472019 · 12 Apr 2019 · Shift 2

   A tuning fork of frequency 480 Hz is used in an experiment for measuring speed of sound (v) in air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column, $l_1=30\text{ cm}$ and $l_2=70\text{ cm}$. Then, v is equal to -

   1. A.$338{\text{ ms}}^{-1}$
   2. B.$384{\text{ ms}}^{-1}$
   3. C.$379{\text{ ms}}^{-1}$
   4. D.$332{\text{ ms}}^{-1}$
   Show answer

   Answer: B

4. Q492019 · 12 Apr 2019 · Shift 2

   A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect 120 dB intensity sound ? [Given reference intensity of sound as $10^{-12}{\text{ W/m}}^2$]

   1. A.20 cm
   2. B.10 cm
   3. C.40 cm
   4. D.30 cm
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   Answer: C

5. Q592019 · 12 Apr 2019 · Shift 2

   Two sources of sound $S_1$ and $S_2$ produce sound waves of same frequency 660 Hz. A listener is moving from source $S_1$ towards $S_2$ with a constant speed u m/s and he hears 10 beats/s. The velocity of sound is 330 m/s. Then, u equals :

   1. A.10.0 m/s
   2. B.5.5 m/s
   3. C.15.0 m/s
   4. D.2.5 m/s
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   Answer: D

6. Q572019 · 10 Apr 2019 · Shift 1

   A stationary source emits sound waves of frequency 500 Hz. Two observers moving along a line passing through the source detect sound to be of frequencies 480 Hz and 530 Hz. Their respective speeds are, in ms–1, (Given speed of sound = 300 m/s)

   1. A.12, 18
   2. B.16, 14
   3. C.12, 16
   4. D.8, 18
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   Answer: A

7. Q422019 · 9 Apr 2019 · Shift 1

   The pressure wave, $P=0.01\sin [1000t-3x]\mathrm{N}{\mathrm{m}}^{-2}$, corresponds to the sound produced by a vibrating blade on a day when atmospheric temperature is 0°C. On some other day, when temperature is T, the speed of sound produced by the same blade and at the same frequency is found to be $336\mathrm{m}{\mathrm{s}}^{-1}$. Approximate value of T is

   1. A.12°C
   2. B.15°C
   3. C.4°C
   4. D.11°C
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   Answer: C

8. Q492019 · 9 Apr 2019 · Shift 1

   A string is clamped at both the ends and it is vibrating in its 4th harmonic. The equation of the stationary wave is $Y=0.3\sin (0.157x)\cos (200\pi t)$. The length of the string is : (All quantities are in SI units.)

   1. A.60 m
   2. B.20 m
   3. C.80 m
   4. D.40 m
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   Answer: C

9. Q602019 · 9 Apr 2019 · Shift 2

   Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of $20\mathrm{m}{\mathrm{s}}^{-1}$ with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency of the sound source in car B ? (speed of sound in air $=340\mathrm{m}{\mathrm{s}}^{-1}$) :-

   1. A.2300 Hz
   2. B.2060 Hz
   3. C.2250 Hz
   4. D.2150 Hz
   Show answer

   Answer: C

10. Q322019 · 12 Jan 2019 · Shift 1

    A person standing on an open ground hears the sound of a jet aeroplane, coming from north at an angle $60^{\circ }$ with ground level. But he finds the aeroplane right vertically above his position. If v is the speed of sound, speed of the plane is :

    1. A.$\frac{\sqrt{3}}{2}v$
    2. B.$\frac{2v}{\sqrt{3}}$
    3. C.$v$
    4. D.$\frac{v}{2}$
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    Answer: D

11. Q422019 · 12 Jan 2019 · Shift 1

    A travelling harmonic wave is represented by the equation $y(x,t)=10^{-3}\sin (50t+2x)$, where, x and y are in metre and t is in seconds. Which of the following is a correct statement about the wave ?

    1. A.The wave is propagating along the positive x-axis with speed $100\mathrm{m}{\mathrm{s}}^{-1}$
    2. B.The wave is propagating along the positive x-axis with speed $25\mathrm{m}{\mathrm{s}}^{-1}$
    3. C.The wave is propagating along the negative x-axis with speed $25\mathrm{m}{\mathrm{s}}^{-1}$
    4. D.The wave is propagating along the negative x-axis with speed $100\mathrm{m}{\mathrm{s}}^{-1}$
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    Answer: C

12. Q472019 · 12 Jan 2019 · Shift 2

    A resonance tube is old and has jagged end. It is still used in the laboratory to determine velocity of sound in air. A tuning fork of frequency 512 Hz produces first resonance when the tube is filled with water to a mark 11 cm below a reference mark, near the open end of the tube. The experiment is repeated with another fork of frequency 256 Hz which produces first resonance when water reaches a mark 27 cm below the reference mark. The velocity of sound in air, obtained in the experiment, is close to :

    1. A.$335\mathrm{m}{\mathrm{s}}^{-1}$
    2. B.$328\mathrm{m}{\mathrm{s}}^{-1}$
    3. C.$341\mathrm{m}{\mathrm{s}}^{-1}$
    4. D.$322\mathrm{m}{\mathrm{s}}^{-1}$
    Show answer

    Answer: B