Sound Waves PYQs Set 4 (PDF)

Set 4 of 9 · Questions 91-120 of 268

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Mere Teacher · Previous Year Questions JEE Main Physics · Sound Waves · Set 4 (Q91-120)
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91. $A musician using an open flute of length 50 cm produces second harmonic sound waves. A person runs towards the musician from another end of a hall at a speed of 10 km / h If the wave speed is 330 m / s, the frequency heard by the running person shall be close to:$ (1) $666 Hz$ (2) $735 Hz$ (3) $753 Hz$ (4) $333 Hz$ 92. $A train moves towards a stationary observer with speed 34 m / s . The train sounds a whistle and its frequency registered by the observer is f_{1} If the speed of the train is reduced to 17 m / s the frequency registered is f_{2} If speed of sound is 340 m / s, then the ratio f_{1} / f_{2} is:$ (1) $18/17$ (2) $19/18$ (3) $20/19$ (4) $21/20$ 93. $The length of a sonometer wire AB is 110 cm. Where should the two bridges be placed from A to divide the wire in 3 segments whose fundamental frequencies are in the ratio of 1:2: 3?$ (1) $60 cm and 90 cm$ (2) $30 cm and 60 cm$ (3) $30 cm and 90 cm$ (4) $40 cm and 80 cm.$ 94. $A traveler is running with velocity v_{0} towards a stationary train. If the train sounds a horn of frequency n then the apparent frequency heard by the traveler will be:$ (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) $none of these$ 95. $A source of sound is moving with a velocity of 50 m s^{- 1} towards a stationary observer. The observer measures the frequency of sound as 500 Hz . The apparent frequency of sound as heard by the observer when source is moving away from him with the same speed is (Speed of sound at room temperature 350 m s^{- 1})$ (1) $400 Hz$ (2) $666 Hz$ (3) $375 Hz$ (4) $177.5 Hz$ 96. $When a source of sound crosses an observer then change in apparent frequency observed by the observer is 2% of its initial frequency. If the speed of sound in 350 m/s then the velocity of source will be -$ (1) $3.5 m/s$ (2) $3.5 cm/s$ (3) $3.5 ft./s$ (4) $zero$ 97. $In the resonance experiment, two air columns (closed at one end) of 100 cm and 120 cm long, give 15 beats per second when each one is sounding in the respective fundamental modes. The velocity of sound in the air column is:$ (1) $370 m / s$ (2) $340 m / s$ (3) $335 m / s$ (4) $360 m / s$ 98. $A pipe open at both ends has a fundamental frequency f in air. The pipe is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now:$ (1) $\frac{3 f}{4}$ (2) $2f$ (3) $f$ (4) $\frac{f}{2}$ 99. $The frequency of the second overtone of the open pipe is equal to the frequency of first overtone of the closed pipe. The ratio of the lengths of the open pipe and the closed pipe is$ (1) $2 : 1$ (2) $1 : 2$ (3) $1 : 3$ (4) $3 : 1$ 100. $A pipe of 30 cm long and open at both the ends produces harmonics. Which harmonic mode of pipe resonates a 1.1 kHz source? Given speed of sound in air = 330 m s^{- 1} .$ (1) $Third harmonic$ (2) $Fifth harmonic$ (3) $Second harmonic$ (4) $Fourth harmonic$ 101. $Two tuning forks, each of frequency 340 Hz, are moving with equal velocity with respect to an observer at rest. One fork is approaching and another is receding away from the observer. The observer is listening beats of frequency 3Hz. If the velocity of sound is 340 m/s then the speed of fork will be -$ (1) $0.4 m/s$ (2) $2.8 m/s$ (3) $4.2 m/s$ (4) $1.5 m/s$ 102. $A fixed source of sound emitting a certain frequency appears as f_{a} when the observer is approaching the source with speed v and frequency f_{r} when the observer recedes from the source with the same speed. The frequency of the source is$ (1) $\frac{f _{r} + f _{a}}{2}$ (2) $\frac{f _{a} - f _{r}}{2}$ (3) $f_{a} f_{r}$ (4) $\frac{2 f _{r} f _{a}}{f _{r} + f _{a}}$ 103. $A bat flies at a steady speed of 4 m s^{- 1} emitting a sound of f = 90 \times 10^{3} Hz . It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as 330 m s^{- 1}).$ (1) $88.1 \times 10^{3} Hz$ (2) $87.1 \times 10^{3} Hz$ (3) $92.1 \times 10^{3} Hz$ (4) $89.1 \times 10^{3} Hz$ 104. $A 5.5 meter length of string has a mass of 0.035 kg . If the tension in the string in 77 N, the speed of a wave on the string is$ (1) $110 m s^{- 1}$ (2) $165 m s^{- 1}$ (3) $77 m s^{- 1}$ (4) $102 m s^{- 1}$ 105. $The ratio of speed of sound in hydrogen gas to the speed of sound in oxygen gas at the same temperature is:$ (1) $1:2$ (2) $4 : 1$ (3) $1:4$ (4) $1 : 1$ 106. $If the end correction of an open pipe is 0.8 cm, then the inner radius of that pipe is$ (1) $\frac{1}{3} cm$ (2) $\frac{2}{3} cm$ (3) $\frac{3}{2} cm$ (4) $0.2 cm$ 107. $A travelling harmonic wave is represented by the equation y (x, t) = 10^{- 3} sin (50 t + 2 x) where x and y are in meter and t is in seconds. Which of the following is a correct statement about the wave?$ (1) $The wave is propagating along the negative x -axis with speed 25 ms^{- 1}$ (2) $The wave is propagating along the positive x -axis with speed 100 ms^{- 1}$ (3) $The wave is propagating along the positive x -axis with speed 25 ms^{- 1}$ (4) $The wave is propagating along the negative x -axis with speed 100 ms^{- 1} .$ 108. $A sound source producing waves of frequency 300 Hz and wavelength 1 m. Observer is stationary, while source is going away with the velocity 30 m/s, then apparent frequency heard by the observer:$ (1) $270 Hz$ (2) $273 Hz$ (3) $383 Hz$ (4) $300 Hz$ 109. $A metal plate of area 1 \times 10^{- 4} m^{2} is illuminated by a radiation of intensity 16 mW / m^{2} . The work function of the metal is 5 eV . The energy of the incident photons is 10 eV and only 10 % of it produces photo electrons. The number of emitted photo electrons per second and their maximum energy respectively, will be: (1 eV = 1.6 \times 10^{- 19} J)$ (1) $10^{14} and 10 eV$ (2) $10^{12} and 5 eV$ (3) $10^{11} and 5 eV$ (4) $10^{10} and 5 eV$ 110. $Two sources of sound placed close to each other are emitting progressive waves given by y_{1} = 4 sin 600 πt and y_{2} = 5 sin 608 πt. An observer located near these two sources of sound will hear:$ (1) $4 beats per second with intensity ratio 25 : 16 between waxing and waning.$ (2) $8 beats per second with intensity ratio 25 : 16 between waxing and waning$ (3) $8 beats per second with intensity ratio 81 : 1 between waxing and waning$ (4) $4 beats per second with intensity ratio 81 : 1 between waxing and waning$ 111. $Two light beams of intensities in the ratio of 9 : 4 are allowed to interfere. The. ratio of the intensity of maxima and minima will be:$ (1) $2:3$ (2) $16:81$ (3) $25: 169$ (4) $25 : 1$ 112. $An observer moves towards a stationary source of sound with a speed 1/5 th of the speed of sound. The wavelength and frequency of the source emitted are λ and f respective. The apparent frequency and wavelength recorded by the observer are respectively: -$ (1) $f, 1.2 λ$ (2) $0.8 f, 0.8 λ$ (3) $1.2 f, 1.2 λ$ (4) $1.2 f, λ$ 113. $Two sound waves with wavelengths 5.0 m and 5.5 m respectively, each propagate in a gas with velocity 330 m / s . We expect the following number of beats per second.$ (1) $6$ (2) $12$ (3) $0$ (4) $1$ 114. $A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 27^{\circ} C, two successive resonances are produced at 20 cm and 73 cm of column length. If the frequency of the tuning fork is 320 Hz, the velocity of sound in air at 27^{\circ} C is [NEET 2018]$ (1) $350 m / s$ (2) $339 m / s$ (3) $330 m / s$ (4) $300 m / s$ 115. $The ratio of frequencies of fundamental harmonic produced by an open pipe to that of closed pipe having the same length is [NEET 2023]$ (1) $2 : 1$ (2) $1 : 3$ (3) $3 : 1$ (4) $1 : 2$ 116. $A stationary source is emitting sound at a fixed frequency f_{0}, which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is 1.2% of f_{0} . What is the difference in the speeds of the cars (in km per hour) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound which is 330 m s^{-1} .$ 117. $A train blowing a whistle of frequency 320 Hz approaches an observer standing on the platform at a speed of 66 m/s. The frequency observed by the observer will be (given speed of sound = 330 m s^{- 1}) Hz.$ 118. $A point source is emitting sound waves of Power 16 \times 10^{- 8} W at the origin. The ratio of intensity (magnitude only) at two points located at a distances of 2 m and 4 m from the origin respectively will be_______Wm^{- 2} .$ 119. $Two tuning forks A and B are sounded together giving rise to 8 beats in 2 s. When fork A is loaded with wax, the beat frequency is reduced to 4 beats in 2 s. If the original frequency of tuning fork B is 380 Hz then original frequency of tuning fork A is____Hz.$ 120. $An organ pipe 40 cm long is open at both ends. The speed of sound in air is 360 m s^{- 1} . The frequency of the second harmonic is__________Hz.$