Sound Waves PYQs Set 1 (PDF)

Set 1 of 8 · Questions 1-30 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Sound Waves · Set 1 (Q1-30)
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1. $The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe. If the length of the closed organ pipe is 20 cm, the length of the open organ pipe is [NEET 2018]$ (1) $12.5 cm$ (2) $8 cm$ (3) $13.3 cm$ (4) $16 cm$ 2. $A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from 440 Hz to 480 Hz, when it gets reflected from the wall. If the speed of sound in air is 345 m / s then the speed of the car is$ (1) $36 km / hr$ (2) $54 km / hr$ (3) $24 km / hr$ (4) $18 km / hr$ 3. $The fundamental frequency of an air column in a pipe closed at one end is 100 Hz . If the same pipe is open at both ends, the frequency produced in Hz are$ (1) $100, 200, 300, 400, \dots$ (2) $100, 300, 500, 700, \dots$ (3) $200, 300, 400, 500, \dots$ (4) $200, 400, 600, 800, \dots$ 4. $An engine is moving towards a wall with a velocity 50 m s^{- 1} emits a note of 1.2 kHz . Speed of sound in air = 350 m s^{- 1} . The frequency of the note after reflection from the wall as heard by the driver of the engine is$ (1) $2.4 kHz$ (2) $0.24 kHz$ (3) $1.6 kHz$ (4) $1.2 kHz$ 5. $A siren placed at a railway platform is emitting sound of frequency 5 kHz. A passenger sitting in a moving train A records a frequency of 5.5 kHz, while the train approaches the siren. During his return journey in a different train B he records a frequency of 6.0 kHz while approaching the same siren. The ratio of the velocity of train B to that of train A is$ (1) $\frac{242}{252}$ (2) $2$ (3) $\frac{5}{6}$ (4) $\frac{11}{6}$ 6. $The speed of sound in oxygen at S.T.P. will be approximately: (Given, R = 8.3 JK^{- 1}, γ = 1.4)$ (1) $310 m / s$ (2) $333 m / s$ (3) $341 m / s$ (4) $325 m / s$ 7. $A train moves towards a stationary observer with speed 34 m / s . The train sounds a whistle and its frequency registered by the observer is f_{1} . If the train's speed is reduced to 17 m / s, the frequency registered is f_{2} . If the speed of sound is 340 m / s then the ratio f_{1} / f_{2} is$ (1) $18/19$ (2) $1/2$ (3) $2$ (4) $19/18$ 8. $With what velocity should an observer approach a stationary sound source so that the apparent frequency of sound should appear double the actual frequency? (v is velocity of sound).$ (1) $2 v$ (2) $v$ (3) $v /2$ (4) $3 v$ 9. $The velocity of sound in any gas depends upon$ (1) $wavelength of sound only$ (2) $density and elasticity of gas$ (3) $intensity of sound waves only$ (4) $amplitude and frequency of sound$ 10. $An air column, closed at one end and open at the other, resonantes with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is:$ (1) $200 cm$ (2) $66.7 cm$ (3) $100 cm$ (4) $150 cm$ 11. $Three sound waves of equal amplitudes have frequencies (n -1), n, (n + 1). They superimpose to give beats. The number of beats produced per second will be$ (1) $2$ (2) $1$ (3) $4$ (4) $3$ 12. $A car is moving towards a high cliff. The driver sounds a horn of frequency f. The reflected sound heard by the driver has frequency 2 f . If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be$ (1) $v / 2$ (2) $v /3$ (3) $v /4$ (4) $v /2$ 13. $The displacement of a wave travelling in the x direction is y = 10^{- 4} sin (600 t - 2 x + \frac{π}{3}) m, where x is in metre and t in second. The speed of the wave is$ (1) $300 m / s$ (2) $200 m / s$ (3) $150 m / s$ (4) $600 m / s$ 14. $The number of possible natural oscillations of air column in a pipe closed at one end of length 85 cm whose frequencies lies below 1250 Hz are: (velocity of sound = 340 m s^{- 1})$ (1) $4$ (2) $5$ (3) $7$ (4) $6$ 15. $A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of15 m s^{- 1} . Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air = 330 m s^{- 1})$ (1) $838 Hz$ (2) $885 Hz$ (3) $765 Hz$ (4) $800 Hz$ 16. $A car is moving towards a high cliff. The car driver sounds horn of frequency ‘f’. The reflected sound heard by the driver has a frequency 2f. If ‘v’ be the velocity of sound then the velocity the car, in the same velocity units, will be:-$ (1) $\frac{v}{3}$ (2) $\frac{v}{4}$ (3) $\frac{v}{2}$ (4) $\frac{v}{2}$ 17. $A person feels 2.5% difference of frequency of a motor-car horn. If the motor-car is moving to the person and the velocity of sound is 320 m/sec, then the velocity of car will be$ (1) $8 m/s (approx.)$ (2) $800 m/s$ (3) $7 m/s$ (4) $6 m/s (approx.)$ 18. $The frequency of a whistle of an engine is 600 cycles/sec is moving with the speed of 30 m/sec towards an observer. The apparent frequency will be (velocity of sound = 330 m/s)$ (1) $600 cps$ (2) $660 cps$ (3) $990 cps$ (4) $330 cps$ 19. $An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?$ (1) $Zero$ (2) $0.5%$ (3) $5%$ (4) $20%$ 20. $A boy is walking away from a wall towards an observer at a speed of 1 meter/sec and blows a whistle whose frequency is 680 Hz. The number of beats heard by the observer per second is (Velocity of sound in air = 340 meters/sec$ (1) $Zero$ (2) $2$ (3) $8$ (4) $4$ 21. $A motor cycle starts from rest and accelerates along a straight path at 2 m/ s^{2} . At the starting point of the motor cycle there is a stationary electric siren. How far has the motor cycle gone when the driver hears the frequency of the siren at 94% of its value when the motor cycle was at rest? (Speed of sound = 330 m s^{-1})$ (1) $98 m$ (2) $147 m$ (3) $196 m$ (4) $49 m$ 22. $A train is moving on a straight track with speed 20 m s^{-1} . It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound = 320 m s^{-1}) close to$ (1) $6%$ (2) $12%$ (3) $18%$ (4) $24%$ 23. $An observer moves towards a stationary source of sound with a velocity equal to one-fifth of the velocity of sound. The percentage change in the frequency will be:$ (1) $20%$ (2) $10%$ (3) $5%$ (4) $0%$ 24. $First overtone frequency of a closed pipe of length l_{1} is equal to the 2^{nd} harmonic frequency of an open pipe of length l_{2} . The ratio l_{1} / l_{2} =$ (1) $¾$ (2) $4/3$ (3) $3/2$ (4) $2/3$ 25. $Two cars moving in opposite directions approach each other with speed of 22 m s^{- 1} and 16.5 m s^{- 1} respectively. The driver ofthe first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is (velocity of sound is 340 m s^{- 1})$ (1) $361 Hz$ (2) $411 Hz$ (3) $448 Hz$ (4) $350 Hz$ 26. $A train moving at a speed of 220 m s^{- 1} towards a stationary object, emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is (Speed of sound in air is 330 m s^{- 1})$ (1) $3500 Hz$ (2) $4000 Hz$ (3) $5000 Hz$ (4) $3000 Hz$ 27. $If the de Broglie wavelength of an electron is equal to 10^{- 3} times the wavelength of a photon of frequency 6 \times 10^{14} then the speed of electron is equal to: (Speed of light (= 3 \times \frac{10 ^{8} m}{s}) Planck's constant = 6.63 \times 10^{- 34} J . s Mass of electron (= 9.1 \times 10^{- 31} kg)$ (1) $1.1 \times 10^{6} m / s$ (2) $1.7 \times 10^{6} m / s$ (3) $1.8 \times 10^{6} m / s$ (4) $1.45 \times 10^{6} m / s$ 28. $A closed organ pipe length ' L_{1}' and an open organ pipe contain diatomic gases of densities ' ρ_{1}' and ' ρ_{2}' respectively. The compressibility’s of the gases are same in both pipes, which are vibrating in their first overtone with same frequency. The length of the open organ pipe is (Neglect end correction)$ (1) $\frac{4 L _{1}}{3}$ (2) $\frac{4 L _{1}}{3} \frac{ρ _{1}}{ρ _{2}}$ (3) $\frac{4 L _{1}}{3} \frac{ρ _{2}}{ρ _{1}}$ (4) $\frac{3}{4 L _{1}} \frac{ρ _{1}}{ρ _{2}}$ 29. $A table is revolving on its axis at 5 revolutions per second. A sound source of frequency 1000 Hz is fixed on the table at 70 cm from the axis. The minimum frequency heard by a listener standing at a distance from the table will be (speed of sound = 352 m/s)$ (1) $1000 Hz$ (2) $1066 Hz$ (3) $941 Hz$ (4) $352 Hz$ 30. $A tuning fork of frequency 480 Hz is used in an experiment for measuring speed of sound (v) in air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column, l_{1} = 30 cm and l_{2} = 70 cm Then, v is equal to:$ (1) $332 ms^{- 1}$ (2) $384 ms^{- 1}$ (3) $338 ms^{- 1}$ (4) $379 ms^{- 1}$