Sound Waves PYQs Set 4 (PDF)

Set 4 of 8 · Questions 91-120 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Sound Waves · Set 4 (Q91-120)
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91. $A pipe open at both ends has a fundamental frequency f in air. The pipe is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now:$ (1) $\frac{3 f}{4}$ (2) $2f$ (3) $f$ (4) $\frac{f}{2}$ 92. $The frequency of the second overtone of the open pipe is equal to the frequency of first overtone of the closed pipe. The ratio of the lengths of the open pipe and the closed pipe is$ (1) $2 : 1$ (2) $1 : 2$ (3) $1 : 3$ (4) $3 : 1$ 93. $A pipe of 30 cm long and open at both the ends produces harmonics. Which harmonic mode of pipe resonates a 1.1 kHz source? Given speed of sound in air = 330 m s^{- 1} .$ (1) $Third harmonic$ (2) $Fifth harmonic$ (3) $Second harmonic$ (4) $Fourth harmonic$ 94. $Two tuning forks, each of frequency 340 Hz, are moving with equal velocity with respect to an observer at rest. One fork is approaching and another is receding away from the observer. The observer is listening beats of frequency 3Hz. If the velocity of sound is 340 m/s then the speed of fork will be -$ (1) $0.4 m/s$ (2) $2.8 m/s$ (3) $4.2 m/s$ (4) $1.5 m/s$ 95. $A fixed source of sound emitting a certain frequency appears as f_{a} when the observer is approaching the source with speed v and frequency f_{r} when the observer recedes from the source with the same speed. The frequency of the source is$ (1) $\frac{f _{r} + f _{a}}{2}$ (2) $\frac{f _{a} - f _{r}}{2}$ (3) $f_{a} f_{r}$ (4) $\frac{2 f _{r} f _{a}}{f _{r} + f _{a}}$ 96. $A bat flies at a steady speed of 4 m s^{- 1} emitting a sound of f = 90 \times 10^{3} Hz . It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as 330 m s^{- 1}).$ (1) $88.1 \times 10^{3} Hz$ (2) $87.1 \times 10^{3} Hz$ (3) $92.1 \times 10^{3} Hz$ (4) $89.1 \times 10^{3} Hz$ 97. $A 5.5 meter length of string has a mass of 0.035 kg . If the tension in the string in 77 N, the speed of a wave on the string is$ (1) $110 m s^{- 1}$ (2) $165 m s^{- 1}$ (3) $77 m s^{- 1}$ (4) $102 m s^{- 1}$ 98. $The ratio of speed of sound in hydrogen gas to the speed of sound in oxygen gas at the same temperature is:$ (1) $1:2$ (2) $4 : 1$ (3) $1:4$ (4) $1 : 1$ 99. $If the end correction of an open pipe is 0.8 cm, then the inner radius of that pipe is$ (1) $\frac{1}{3} cm$ (2) $\frac{2}{3} cm$ (3) $\frac{3}{2} cm$ (4) $0.2 cm$ 100. $A travelling harmonic wave is represented by the equation y (x, t) = 10^{- 3} sin (50 t + 2 x) where x and y are in meter and t is in seconds. Which of the following is a correct statement about the wave?$ (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) $The wave is propagating along the negative x -axis with speed 100 ms^{- 1} .$ 101. $A sound source producing waves of frequency 300 Hz and wavelength 1 m. Observer is stationary, while source is going away with the velocity 30 m/s, then apparent frequency heard by the observer:$ (1) $270 Hz$ (2) $273 Hz$ (3) $383 Hz$ (4) $300 Hz$ 102. $A metal plate of area 1 \times 10^{- 4} m^{2} is illuminated by a radiation of intensity 16 mW / m^{2} . The work function of the metal is 5 eV . The energy of the incident photons is 10 eV and only 10 % of it produces photo electrons. The number of emitted photo electrons per second and their maximum energy respectively, will be: (1 eV = 1.6 \times 10^{- 19} J)$ (1) $10^{14} and 10 eV$ (2) $10^{12} and 5 eV$ (3) $10^{11} and 5 eV$ (4) $10^{10} and 5 eV$ 103. $Two sources of sound placed close to each other are emitting progressive waves given by y_{1} = 4 sin 600 πt and y_{2} = 5 sin 608 πt. An observer located near these two sources of sound will hear:$ (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) $4 beats per second with intensity ratio 81 : 1 between waxing and waning$ 104. $Two light beams of intensities in the ratio of 9 : 4 are allowed to interfere. The. ratio of the intensity of maxima and minima will be:$ (1) $2:3$ (2) $16:81$ (3) $25: 169$ (4) $25 : 1$ 105. $An observer moves towards a stationary source of sound with a speed 1/5 th of the speed of sound. The wavelength and frequency of the source emitted are λ and f respective. The apparent frequency and wavelength recorded by the observer are respectively: -$ (1) $f, 1.2 λ$ (2) $0.8 f, 0.8 λ$ (3) $1.2 f, 1.2 λ$ (4) $1.2 f, λ$ 106. $Two sound waves with wavelengths 5.0 m and 5.5 m respectively, each propagate in a gas with velocity 330 m / s . We expect the following number of beats per second.$ (1) $6$ (2) $12$ (3) $0$ (4) $1$ 107. $A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 27^{\circ} C, two successive resonances are produced at 20 cm and 73 cm of column length. If the frequency of the tuning fork is 320 Hz, the velocity of sound in air at 27^{\circ} C is [NEET 2018]$ (1) $350 m / s$ (2) $339 m / s$ (3) $330 m / s$ (4) $300 m / s$ 108. $The ratio of frequencies of fundamental harmonic produced by an open pipe to that of closed pipe having the same length is [NEET 2023]$ (1) $2 : 1$ (2) $1 : 3$ (3) $3 : 1$ (4) $1 : 2$ 109. $Two tuning forks, A and B, produce notes of frequencies 258 Hz and 262 Hz . An unknown note sounded with A produces certain beats. When the same note is sounded with B, the beat frequency gets doubled. The unknown frequency is$ (1) $250 Hz$ (2) $252 Hz$ (3) $254 Hz$ (4) $256 Hz$ 110. $A train is approaching towards a platform with a speed of 10 m s^{- 1} while blowing a whistle of frequency 340 Hz . What is the frequency of whistle heard by a stationary observer on the platform? Given speed of sound = 340 m s^{- 1} .$ (1) $340 Hz$ (2) $360 Hz$ (3) $330 Hz$ (4) $350 Hz$ 111. $When the observer moves towards the stationary source with velocity, V_{1}, the apparent frequency of emitted note is F_{1} . When the observer moves away from the source with velocity V_{1}, the apparent frequency is F_{2} . If V is the velocity of sound in air and \frac{F _{1}}{F _{2}} = 2 then \frac{V}{V _{1}} = ?$ (1) $2$ (2) $3$ (3) $4$ (4) $5$ 112. $The pitch of the whistle of an engine appears to drop to (\frac{5}{6})^{th} of original value when it passes a stationary observer. If the speed of sound in air is 350 m / s then the speed of engine is$ (1) $35 m / s$ (2) $70 m / s$ (3) $105 m / s$ (4) $140 m / s$ 113. $In a pipe open at both ends, ' n_{1}' and ' n_{2}' be the frequencies corresponding to vibrating lengths ' l_{1}' and ' l_{2}' respectively. The end correction is$ (1) $\frac{n _{1} l _{1} - n _{2} l _{2}}{2 ( n _{1} - n _{2} )}$ (2) $\frac{n _{2} l _{2} - n _{1} l _{1}}{2 ( n _{2} - n _{1} )}$ (3) $\frac{n _{2} l _{2} - n _{1} l _{1}}{2 ( n _{1} - n _{2} )}$ (4) $\frac{n _{1} l _{1} - n _{2} l _{2}}{( n _{1} - n _{2} )}$ 114. $An observer moves towards a stationary source of sound of frequency n. The apparent frequency heard by him is 2n. If the velocity of sound in air is 332 m/sec, then the velocity of the observer is$ (1) $166 m/sec$ (2) $664 m/sec$ (3) $332 m/sec$ (4) $1328 m/sec$ 115. $A hospital uses an ultrasonic scanner to locate tumors in a tissue. The operating frequency of the scanner is 4.2 MHz . The speed of sound in a tissue is 1.7 km / s . The wavelength of sound in the tissue is close to$ (1) $4 \times 1 0^{- 3} m$ (2) $8 \times 1 0^{- 3} m$ (3) $4 \times 1 0^{- 4} m$ (4) $8\times 1 0^{- 4} m.$ 116. $A tuning fork A of unknown frequency produces 5 beats/s with a fork of known frequency 340 Hz . When fork A is filed, the beat frequency decreases to 2 beats/s. What is the frequency of fork A ?$ (1) $335 Hz$ (2) $345 Hz$ (3) $338 Hz$ (4) $342 Hz$ 117. $A closed organ pipe and an open organ pipe of same length produce 2 beats/second while vibrating in their fundamental modes. The length of the open organ pipe is halved and that of closed pipe is doubled. Then, the number of beats produced per second while vibrating in the fundamental mode is$ (1) $2$ (2) $6$ (3) $8$ (4) $7$ 118. $The two nearest harmonics of a tube closed at one end and open at another end are 220 Hz and 260 Hz. What is the fundamental frequency of the system?$ (1) $20 Hz$ (2) $30 Hz$ (3) $40 Hz$ (4) $10 Hz$ 119. $A pipe closed at one end has length 0.8 m . At its open end a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire in 50 N and the speed of sound is 320 m / s, the mass of the string used is$ (1) $4 gram$ (2) $8 gram$ (3) $10 gram$ (4) $12 gram$ 120. $Train A and train B are running on parallel tracks in the opposite directions with speeds of 36 km / hour and 72 km / hour, respectively. A person is walking in train A in the direction opposite to its motion with a speed of 1.8 km / hour . Speed (in ms^{- 1}) of this person as observed from train B will be close to: (take the distance between the tracks as negligible)$ (1) $30.5 ms^{- 1}$ (2) $29.5 ms^{- 1}$ (3) $31.5 ms^{- 1}$ (4) $28.5 ms^{- 1}$