Sound Waves PYQs Set 3 (PDF)

Set 3 of 8 · Questions 61-90 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Sound Waves · Set 3 (Q61-90)
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61. $A whistle sends out 256 waves in a second. If the whistle approaches the observer with velocity 1/3 of the velocity of sound in air, the number of waves per second the observer will receive$ (1) $384$ (2) $192$ (3) $300$ (4) $200$ 62. $A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer if f_{1} . If the speed of the train is reduced to 17 m/s, the frequency registered is f_{2} . If speed of sound is 340 m/s, then the ratio f_{1} / f_{2} is:$ (1) $\frac{20}{19}$ (2) $\frac{18}{17}$ (3) $\frac{19}{18}$ (4) $\frac{21}{20}$ 63. $Three sound waves of equal amplitudes have frequencies (n - 1), n, (n + 1) . They superimpose to give beats. The number of beats produced per second will be [NEET 2016]$ (1) $1$ (2) $4$ (3) $3$ (4) $2$ 64. $A source is approaching a stationary observer with velocity (\frac{1}{10})^{th} that of sound. Ratio of observed and real frequencies will be:$ (1) $\frac{9}{10}$ (2) $\frac{11}{10}$ (3) $\frac{10}{11}$ (4) $\frac{10}{9}$ 65. $When open pipe is closed from one end then third overtone of closed pipe is higher in frequency by 150 Hz than second overtone of open pipe. The fundamental frequency of open end pipe will be$ (1) $75 Hz$ (2) $150 Hz$ (3) $225 Hz$ (4) $300 Hz$ 66. $A stretched wire of length 260 cm is set into vibrations. It is divided into three segments whose frequencies are in the ratio 2 : 3 : 4 . Their lengths must be$ (1) $80 cm, 60 cm, 120 cm$ (2) $120 cm, 80 cm, 60 cm$ (3) $60 cm, 80 cm, 120 cm$ (4) $120 cm, 60 cm, 80 cm$ 67. $An observer moves towards a stationary source of sound with a speed 1/ 5^{th} ofthe speed ofsound. The wavelength and frequency of the source emitted are λ and f respectively. The apparent frequency and wavelength recorded by the observer are respectively$ (1) $1.2 f, 1.2 λ$ (2) $1.2 f, λ$ (3) $f 1.2 M$ (4) $0.8 f, 0.8 λ$ 68. $Each of the two strings of length 51.6 cm and 49.1 cm are tensioned separately by 20 N force. Mass per unit length of both the strings is same and equal to 1g/m. When both the strings vibrate simultaneously the number of beats is$ (1) $7$ (2) $8$ (3) $3$ (4) $5$ 69. $A source of frequency 150 Hz is moving in the direction of a person with a velocity of 110 m/s. The frequency heard by the person will be (speed of sound in medium = 330 m/s)$ (1) $225 Hz$ (2) $200 Hz$ (3) $150 Hz$ (4) $100 Hz$ 70. $A pipe closed at one end has length 83 cm . The number of possible natural oscillations of air column whose frequencies lie below 1000 Hz are (velocity of sound in air = 332 m / s)$ (1) $3$ (2) $4$ (3) $5$ (4) $6$ 71. $A whistle giving out 450 Hz approaches a stationary observer at a speed of 33 m/s. The frequency heard by the observer in Hz is$ (1) $409$ (2) $429$ (3) $517$ (4) $500$ 72. $The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe. If the length of the closed organ pipe is 20 cm, the length of the open organ pipe is$ (1) $13.2 cm$ (2) $8 cm$ (3) $12.5 cm$ (4) $16 cm$ 73. $In fundamental mode, the time required for the sound wave to reach up to the closed end of a pipe filled with air is ' t' second. The frequency of vibration of air column is$ (1) $(2 t)^{- 1}$ (2) $2 (t)^{- 1}$ (3) $4 (t)^{- 1}$ (4) $(4 t)^{- 1}$ 74. $A source emitting a note of frequency 240 Hz is moving towards an observer with a speed of 20 m/s. If the observer also moves with a speed of 20 m/s towards the source, the apparent frequency heard by observer is (velocity of sound = 340 m/s)$ (1) $270 Hz$ (2) $240 Hz$ (3) $268 Hz$ (4) $360 Hz$ 75. $The driver of a bus approaching a big wall notices that the frequency of his bus's horn changes from 420 Hz to 490Hz when he hears it after it gets reflected from the wall. Find the speed of the bus if speed of the sound is 330 ms^{- 1}$ (1) $61 kmh^{- 1}$ (2) $91 kmh^{- 1}$ (3) $81 kmh^{- 1}$ (4) $71 kmh^{- 1}$ 76. $The engine of a train moving with speed 10 m s^{- 1} towards a platform sounds a whistle at frequency 400 Hz. The frequency heard by a passenger inside the train is: (Neglect air speed. Speed of sound in air = 330 m s^{- 1})$ (1) $400 Hz$ (2) $200 Hz$ (3) $412 Hz$ (4) $388 Hz$ 77. $A closed organ pipe has a fundamental frequency of 1.5 kHz . The number of overtones that can be distinctly heard by a person with this organ pipe will be: (Assume that the highest frequency a person can hear is 20, 000 Hz)$ (1) $6$ (2) $4$ (3) $7$ (4) $5$ 78. $A source of sound is moving with constant velocity of 20 m/s emitting a note of frequency 1000 Hz. The ratio of frequencies observed by a stationary observer while the source is approaching him and after it crosses him will be (Speed of sound v = 340 m/s)$ (1) $9 : 8$ (2) $8 : 9$ (3) $1 : 1$ (4) $9 : 10$ 79. $At what speed should a source of sound move so that stationary observer finds the apparent frequency equal to half of the original frequency$ (1) $\frac{v}{2}$ (2) $2v$ (3) $\frac{v}{4}$ (4) $v$ 80. $A train moving at a speed of 220 m s^{-1} towards a stationary object, emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the of the train is:$ (1) $3500 Hz$ (2) $4000 Hz$ (3) $5000 Hz$ (4) $3000 Hz$ 81. $A person observes two moving trains, 'A' reaching the station and 'B' leaving the station with equal speed of 30 m/s. If both trains emit sounds with frequency 300 Hz, (Speed of sound: 330 m/s) approximate difference of frequencies heard by the person will be:$ (1) $33 Hz$ (2) $55 Hz$ (3) $80 Hz$ (4) $10 Hz$ 82. $The number of possible natural oscillations of air column in a pipe closed at one end of length 85 cm whose frequencies lie below 1250 Hz are (Velocity of sound = 340 m s^{- 1})$ (1) $4$ (2) $5$ (3) $7$ (4) $6$ 83. $The Fundamental frequency of a closed organ pipe of length 20 cm is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both the ends is:$ (1) $100 cm$ (2) $120 cm$ (3) $140 cm$ (4) $80 cm$ 84. $A musician using an open flute of length 50 cm produces second harmonic sound waves. A person runs towards the musician from another end of a hall at a speed of 10 km / h If the wave speed is 330 m / s, the frequency heard by the running person shall be close to:$ (1) $666 Hz$ (2) $735 Hz$ (3) $753 Hz$ (4) $333 Hz$ 85. $A train moves towards a stationary observer with speed 34 m / s . The train sounds a whistle and its frequency registered by the observer is f_{1} If the speed of the train is reduced to 17 m / s the frequency registered is f_{2} If speed of sound is 340 m / s, then the ratio f_{1} / f_{2} is:$ (1) $18/17$ (2) $19/18$ (3) $20/19$ (4) $21/20$ 86. $The length of a sonometer wire AB is 110 cm. Where should the two bridges be placed from A to divide the wire in 3 segments whose fundamental frequencies are in the ratio of 1:2: 3?$ (1) $60 cm and 90 cm$ (2) $30 cm and 60 cm$ (3) $30 cm and 90 cm$ (4) $40 cm and 80 cm.$ 87. $A traveler is running with velocity v_{0} towards a stationary train. If the train sounds a horn of frequency n then the apparent frequency heard by the traveler will be:$ (1) $n’ = n (\frac{v + v _{0}}{v})$ (2) $n’ = n (\frac{v - v _{0}}{v + v _{s}})$ (3) $n’ = n (\frac{v + v _{0}}{v}) +vs$ (4) $none of these$ 88. $A source of sound is moving with a velocity of 50 m s^{- 1} towards a stationary observer. The observer measures the frequency of sound as 500 Hz . The apparent frequency of sound as heard by the observer when source is moving away from him with the same speed is (Speed of sound at room temperature 350 m s^{- 1})$ (1) $400 Hz$ (2) $666 Hz$ (3) $375 Hz$ (4) $177.5 Hz$ 89. $When a source of sound crosses an observer then change in apparent frequency observed by the observer is 2% of its initial frequency. If the speed of sound in 350 m/s then the velocity of source will be -$ (1) $3.5 m/s$ (2) $3.5 cm/s$ (3) $3.5 ft./s$ (4) $zero$ 90. $In the resonance experiment, two air columns (closed at one end) of 100 cm and 120 cm long, give 15 beats per second when each one is sounding in the respective fundamental modes. The velocity of sound in the air column is:$ (1) $370 m / s$ (2) $340 m / s$ (3) $335 m / s$ (4) $360 m / s$