Sound Waves PYQs Set 5 (PDF)

Set 5 of 9 · Questions 121-150 of 268

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Mere Teacher · Previous Year Questions JEE Main Physics · Sound Waves · Set 5 (Q121-150)
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121. $Two tuning forks, A and B, produce notes of frequencies 258 Hz and 262 Hz . An unknown note sounded with A produces certain beats. When the same note is sounded with B, the beat frequency gets doubled. The unknown frequency is$ (1) $250 Hz$ (2) $252 Hz$ (3) $254 Hz$ (4) $256 Hz$ 122. $A train is approaching towards a platform with a speed of 10 m s^{- 1} while blowing a whistle of frequency 340 Hz . What is the frequency of whistle heard by a stationary observer on the platform? Given speed of sound = 340 m s^{- 1} .$ (1) $340 Hz$ (2) $360 Hz$ (3) $330 Hz$ (4) $350 Hz$ 123. $When the observer moves towards the stationary source with velocity, V_{1}, the apparent frequency of emitted note is F_{1} . When the observer moves away from the source with velocity V_{1}, the apparent frequency is F_{2} . If V is the velocity of sound in air and \frac{F _{1}}{F _{2}} = 2 then \frac{V}{V _{1}} = ?$ (1) $2$ (2) $3$ (3) $4$ (4) $5$ 124. $The pitch of the whistle of an engine appears to drop to (\frac{5}{6})^{th} of original value when it passes a stationary observer. If the speed of sound in air is 350 m / s then the speed of engine is$ (1) $35 m / s$ (2) $70 m / s$ (3) $105 m / s$ (4) $140 m / s$ 125. $In a pipe open at both ends, ' n_{1}' and ' n_{2}' be the frequencies corresponding to vibrating lengths ' l_{1}' and ' l_{2}' respectively. The end correction is$ (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) $\frac{n _{1} l _{1} - n _{2} l _{2}}{( n _{1} - n _{2} )}$ 126. $An observer moves towards a stationary source of sound of frequency n. The apparent frequency heard by him is 2n. If the velocity of sound in air is 332 m/sec, then the velocity of the observer is$ (1) $166 m/sec$ (2) $664 m/sec$ (3) $332 m/sec$ (4) $1328 m/sec$ 127. $A hospital uses an ultrasonic scanner to locate tumors in a tissue. The operating frequency of the scanner is 4.2 MHz . The speed of sound in a tissue is 1.7 km / s . The wavelength of sound in the tissue is close to$ (1) $4 \times 1 0^{- 3} m$ (2) $8 \times 1 0^{- 3} m$ (3) $4 \times 1 0^{- 4} m$ (4) $8\times 1 0^{- 4} m.$ 128. $A tuning fork A of unknown frequency produces 5 beats/s with a fork of known frequency 340 Hz . When fork A is filed, the beat frequency decreases to 2 beats/s. What is the frequency of fork A ?$ (1) $335 Hz$ (2) $345 Hz$ (3) $338 Hz$ (4) $342 Hz$ 129. $A closed organ pipe and an open organ pipe of same length produce 2 beats/second while vibrating in their fundamental modes. The length of the open organ pipe is halved and that of closed pipe is doubled. Then, the number of beats produced per second while vibrating in the fundamental mode is$ (1) $2$ (2) $6$ (3) $8$ (4) $7$ 130. $The two nearest harmonics of a tube closed at one end and open at another end are 220 Hz and 260 Hz. What is the fundamental frequency of the system?$ (1) $20 Hz$ (2) $30 Hz$ (3) $40 Hz$ (4) $10 Hz$ 131. $A pipe closed at one end has length 0.8 m . At its open end a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire in 50 N and the speed of sound is 320 m / s, the mass of the string used is$ (1) $4 gram$ (2) $8 gram$ (3) $10 gram$ (4) $12 gram$ 132. $Train A and train B are running on parallel tracks in the opposite directions with speeds of 36 km / hour and 72 km / hour, respectively. A person is walking in train A in the direction opposite to its motion with a speed of 1.8 km / hour . Speed (in ms^{- 1}) of this person as observed from train B will be close to: (take the distance between the tracks as negligible)$ (1) $30.5 ms^{- 1}$ (2) $29.5 ms^{- 1}$ (3) $31.5 ms^{- 1}$ (4) $28.5 ms^{- 1}$ 133. $A police van moving with velocity 22 m/s and emitting sound of frequency 176 Hz, follows a motorcycle which is moving towards a stationary car and away from the police van. The stationary car is emitting frequency 165 Hz. Speed of sound air is 330 m/s. If motorcyclist does not hear any beats, then his velocity is$ (1) $33 m/s$ (2) $22 m/s$ (3) $11 m/s$ (4) $0$ 134. $4.0 g of a gas occupies 22.4 liters at NTP. The specific heat capacity of the gas at constant volume is 5.0JK-1. IF the speed of sound in this gas at NTP is 952 ms^{- 1}, then the heat capacity at constant pressure is (Take gas constant R = 8.3 JK^{- 1} mol^{- 1})$ (1) $7.5 JK^{- 1} mol^{- 1}$ (2) $7.0 JK^{- 1} mol^{- 1}$ (3) $8.5 JK^{- 1} mol^{- 1}$ (4) $8.0 JK^{- 1} mol^{- 1}$ 135. $A submarine (A) travelling at 18 km / h is being chased along the line of its velocity by another submarine (B) travelling at 27 km / hr . B sends a sonar signal of 500 Hz to detect A and receives a reflected sound of frequency v . The value of v is close to (Speed of sound in water = 1500 ms^{- 1})$ (1) $504 Hz$ (2) $507 Hz$ (3) $499 Hz$ (4) $502 Hz$ 136. $A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect 120 dB intensity sound? [Given reference intensity of sound as 10^{- 12} W / m^{2}]$ (1) $40 cm$ (2) $20 cm$ (3) $10 cm$ (4) $30 cm$ 137. $A source S having frequency 600 Hz is kept at rest at bottom of a flowing river. Find out the frequency detected by a stationary detector present above the river in air. [Velocity of sound in water = 1500 m/s; velocity of sound in air = 300 m/s]$ (1) $1500 Hz$ (2) $600 Hz$ (3) $1200 Hz$ (4) $300 Hz$ 138. $If the length of an open organ pipe is 33.3 cm, then the frequency of fifth overtone is [Neglect end correction, velocity of sound = 333 m / s]$ (1) $3500 Hz$ (2) $3000 Hz$ (3) $2500 Hz$ (4) $2000 Hz$ 139. $The change in frequency due to Doppler effect does not depend on$ (1) $the speed of the source$ (2) $the speed of the observer$ (3) $the frequency of the source$ (4) $separation between the source and the observer$ 140. $An air column, closed at one end and open at the other, resonates with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is$ (1) $150 cm$ (2) $200 cm$ (3) $66.7 cm$ (4) $100 cm$ 141. $In a guitar, two strings A and B made of same material are slightly out of tune and produce beats of frequency 6 Hz. When tension in B is slightly decreased, the beat frequency increases to 7 Hz. If the frequency of A is 530 Hz, the original frequency of B will be [NEET 2020]$ (1) $524 Hz$ (2) $536 Hz$ (3) $537 Hz$ (4) $523 Hz$ 142. $Two trains move towards each other with the same speed. The speed of sound is 340 m / s . If the height ofthe tone of the whistle of one of them heard on the other changes to 9/8 times, then the speed of each train should be$ (1) $20 m / s$ (2) $2 m / s$ (3) $200 m / s$ (4) $2000 m / s$ 143. $A source of sound and listener are approaching each other with a speed of 40 m/s. The apparent frequency of note produced by the source is 400 cps. Then, its true frequency (in cps) is (velocity of sound in air = 360 m/s)$ (1) $420$ (2) $360$ (3) $400$ (4) $320$ 144. $A tuning fork A produces 4 beats per second with another tuning fork B of frequency 320 Hz . On filing one of the prongs of A, 4 beats per second are again heard when sounded with the same fork B. Then the frequency of the fork A before filing is$ (1) $328 Hz$ (2) $316 Hz$ (3) $324 Hz$ (4) $320 Hz$ 145. $A source of sound S is moving with a velocity of 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz . What will be the apparent frequency of the source when it is moving away from the observer after crossing him? (Take velocity of sound in air 350 m/s$ (1) $750 Hz$ (2) $857 Hz$ (3) $1143 Hz$ (4) $807 Hz$ 146. $Two sources P and Q produce notes offrequency 660 Hz each. Alistener moves from P to Q with a speed of 1 m s^{- 1} . If the speed of sound is 330 m / s, then the number of beats heard by the listener per second will be$ (1) $4$ (2) $8$ (3) $2$ (4) $zero$ 147. $Two waves of lengths 50 cm and 51 cm produced 12 beats per sec. The velocity of sound is$ (1) $340 m / s$ (2) $331 m / s$ (3) $306 m / s$ (4) $360 m / s$ 148. $A tuning fork P of unknown frequency gives 7 beats in 2 sec with another tuning fork Q. When Q runs towards the wall with a speed of 5 m/s it gives 5 beats per sec with its echo. On loading wax on P it gives 5 beats per second with Q. What is the original frequency of P? Assume speed of sound = 332 m/s.$ 149. $Two open organ pipes of lengths 60 cm and 90 cm resonate at 6^{th} and 5^{th} harmonics respectively. The difference of frequencies for the given modes is____Hz . (Velocity of sound in air = 333 m / s)$ 150. $The first overtone frequency of an open organ pipe is equal to the fundamental frequency of a closed organ pipe. If the length of the closed organ pipe is 20 cm. The length of the open organ pipe is_____ cm.$