Sound Waves PYQs Set 5 (PDF)

Set 5 of 8 · Questions 121-150 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Sound Waves · Set 5 (Q121-150)
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121. $A police van moving with velocity 22 m/s and emitting sound of frequency 176 Hz, follows a motorcycle which is moving towards a stationary car and away from the police van. The stationary car is emitting frequency 165 Hz. Speed of sound air is 330 m/s. If motorcyclist does not hear any beats, then his velocity is$ (1) $33 m/s$ (2) $22 m/s$ (3) $11 m/s$ (4) $0$ 122. $4.0 g of a gas occupies 22.4 liters at NTP. The specific heat capacity of the gas at constant volume is 5.0JK-1. IF the speed of sound in this gas at NTP is 952 ms^{- 1}, then the heat capacity at constant pressure is (Take gas constant R = 8.3 JK^{- 1} mol^{- 1})$ (1) $7.5 JK^{- 1} mol^{- 1}$ (2) $7.0 JK^{- 1} mol^{- 1}$ (3) $8.5 JK^{- 1} mol^{- 1}$ (4) $8.0 JK^{- 1} mol^{- 1}$ 123. $A submarine (A) travelling at 18 km / h is being chased along the line of its velocity by another submarine (B) travelling at 27 km / hr . B sends a sonar signal of 500 Hz to detect A and receives a reflected sound of frequency v . The value of v is close to (Speed of sound in water = 1500 ms^{- 1})$ (1) $504 Hz$ (2) $507 Hz$ (3) $499 Hz$ (4) $502 Hz$ 124. $A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect 120 dB intensity sound? [Given reference intensity of sound as 10^{- 12} W / m^{2}]$ (1) $40 cm$ (2) $20 cm$ (3) $10 cm$ (4) $30 cm$ 125. $A source S having frequency 600 Hz is kept at rest at bottom of a flowing river. Find out the frequency detected by a stationary detector present above the river in air. [Velocity of sound in water = 1500 m/s; velocity of sound in air = 300 m/s]$ (1) $1500 Hz$ (2) $600 Hz$ (3) $1200 Hz$ (4) $300 Hz$ 126. $If the length of an open organ pipe is 33.3 cm, then the frequency of fifth overtone is [Neglect end correction, velocity of sound = 333 m / s]$ (1) $3500 Hz$ (2) $3000 Hz$ (3) $2500 Hz$ (4) $2000 Hz$ 127. $The change in frequency due to Doppler effect does not depend on$ (1) $the speed of the source$ (2) $the speed of the observer$ (3) $the frequency of the source$ (4) $separation between the source and the observer$ 128. $An air column, closed at one end and open at the other, resonates with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is$ (1) $150 cm$ (2) $200 cm$ (3) $66.7 cm$ (4) $100 cm$ 129. $In a guitar, two strings A and B made of same material are slightly out of tune and produce beats of frequency 6 Hz. When tension in B is slightly decreased, the beat frequency increases to 7 Hz. If the frequency of A is 530 Hz, the original frequency of B will be [NEET 2020]$ (1) $524 Hz$ (2) $536 Hz$ (3) $537 Hz$ (4) $523 Hz$ 130. $Two trains move towards each other with the same speed. The speed of sound is 340 m / s . If the height ofthe tone of the whistle of one of them heard on the other changes to 9/8 times, then the speed of each train should be$ (1) $20 m / s$ (2) $2 m / s$ (3) $200 m / s$ (4) $2000 m / s$ 131. $A source of sound and listener are approaching each other with a speed of 40 m/s. The apparent frequency of note produced by the source is 400 cps. Then, its true frequency (in cps) is (velocity of sound in air = 360 m/s)$ (1) $420$ (2) $360$ (3) $400$ (4) $320$ 132. $A tuning fork A produces 4 beats per second with another tuning fork B of frequency 320 Hz . On filing one of the prongs of A, 4 beats per second are again heard when sounded with the same fork B. Then the frequency of the fork A before filing is$ (1) $328 Hz$ (2) $316 Hz$ (3) $324 Hz$ (4) $320 Hz$ 133. $A source of sound S is moving with a velocity of 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz . What will be the apparent frequency of the source when it is moving away from the observer after crossing him? (Take velocity of sound in air 350 m/s$ (1) $750 Hz$ (2) $857 Hz$ (3) $1143 Hz$ (4) $807 Hz$ 134. $Two sources P and Q produce notes offrequency 660 Hz each. Alistener moves from P to Q with a speed of 1 m s^{- 1} . If the speed of sound is 330 m / s, then the number of beats heard by the listener per second will be$ (1) $4$ (2) $8$ (3) $2$ (4) $zero$ 135. $Two waves of lengths 50 cm and 51 cm produced 12 beats per sec. The velocity of sound is$ (1) $340 m / s$ (2) $331 m / s$ (3) $306 m / s$ (4) $360 m / s$ 136. $Two stationary sources each emitting waves of wavelength λ, an observer moves from one source to another with velocity u . Then number of beats heard by him$ (1) $\frac{2 u}{λ}$ (2) $\frac{u}{λ}$ (3) $uλ$ (4) $\frac{u}{2 λ}$ 137. $Sound waves of frequency 600 Hz fall normally on a perfectly reflecting wall. The shortest distance from the wall at which all particles will have maximum amplitude of vibration is (speed of sound = 300 m s^{- 1})$ (1) $\frac{1}{4} m$ (2) $\frac{1}{8} m$ (3) $\frac{3}{8} m$ (4) $\frac{7}{8} m$ 138. $There is one closed pipe whose third overtone is in resonance with the upper string, which is in the 4^{th} overtones with an open pipe, then$ (1) $2 n = 3 m$ (2) $5 n = 7 m$ (3) $3 n = 5 m$ (4) $7 n = 5 m$ 139. $A point source is kept at the center of a spherically enclosed detector. If the volume of the detector increased by 8 times, the intensity will$ (1) $increase by 64 times$ (2) $increase by 8 times$ (3) $decrease by 4 times$ (4) $decrease by 8 times$ 140. $A pipe open at both ends has fundamental frequency f in air. The pipe is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now:$ (1) $\frac{3 f}{4}$ (2) $2 f$ (3) $f$ (4) $\frac{f}{2}$ 141. $Wire having tension 225 N produces six beats per second when it is tuned with a fork. When tension changes to 256 N, it is tuned with the same fork, the number of beats remain unchanged. The frequency of the fork will be$ (1) $186 Hz$ (2) $225 Hz$ (3) $256 Hz$ (4) $280 Hz$ 142. $A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of:$ (1) $1000$ (2) $10000$ (3) $10$ (4) $100$ 143. $A sound wave of frequency 245 Hz travelswith the speed of 300 ms^{- 1} along the positive x - axis. Each point of the wave moves to and for through a total distance of 6 cm . What will be the mathematical expression of this travelling wave?$ (1) $Y (x, t) = 0.03 (sin 5.1 x - (0.2 \times 10^{3}) t)$ (2) $Y (x, t) = 0.06 (sin 5.1 x - (1.5 \times 10^{3}) t)$ (3) $Y (x, t) = 0.06 (sin 0.8 x - (0.5 \times 10^{3}) t)$ (4) $Y (x, t) = 0.03 (sin 5.1 x - (1.5 \times 10^{3}) t)$ 144. $The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe. If the length of the closed organ pipe is 20 cm, the length of the open organ pipe is$ (1) $13.3 cm$ (2) $16 cm$ (3) $12.5 cm$ (4) $8 cm$ 145. $Two sound sources S_{1} and S_{2} of frequencies 324 Hz and 320 Hz are placed at certain separation. An observer is moving away from S_{1} and towards S_{2} on line joining them. If he hears no beats then speed of observer is (v = 344 m/sec):$ (1) $20 m/s$ (2) $10 m/s$ (3) $5 m/s$ (4) $2.1 m/s$ 146. $The transverse displacement y(x,t) of a wave on a string is given by y (x, t) = e^{- (a x^{2} + b t^{2} + 2 ab xt)} This represents a:$ (1) $wave moving in +x-direction with speed \frac{a}{b}$ (2) $wave moving in -x-direction with speed \frac{b}{a}$ (3) $standing wave of frequency b$ (4) $standing wave of frequency \frac{1}{b}$ 147. $A cylindrical tube, open at both ends has fundamental frequency f in air. The tube is dipped vertically in water, so that half of it is in water. The fundamental frequency ofair column is now$ (1) $f /2$ (2) $3 f /4$ (3) $2 f$ (4) $f$ 148. $An open pipe and a closed pipe are in resonance with each other with their first overtones. The ratio of their lengths our$ (1) $4 : 3$ (2) $3 : 4$ (3) $1 : 3$ (4) $3 : 5$ 149. $A student is performing the experiment of Resonance Column. The diameter of the column tube is 4cm. The distance frequency of the tuning fork is 512 Hz. The air temperature is 38°C in which the speed of sound is 336 m/s. The zero of the meter scale coincides with the top end of the Resonance column. When first resonance occurs, the reading of the water level in the column is$ (1) $14.0$ (2) $15.2$ (3) $16.4$ (4) $17.6$ 150. $In the case of sound waves, wind is blowing from source to receiver with speed U_{W} . Both source and receiver are stationary. If λ_{0} is the original wavelength with no wind and V is speed of sound in air then wavelength as received by the receiver is given by:$ (1) $λ_{0}$ (2) $V+UwV λ_{0}$ (3) $V-UwV λ_{0}$ (4) $VV+Vw λ_{0}$