Sound Waves PYQs Set 8 (PDF)

Set 8 of 9 · Questions 211-240 of 268

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Mere Teacher · Previous Year Questions JEE Main Physics · Sound Waves · Set 8 (Q211-240)
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211. $A car P travelling at 20 m s^{- 1} sounds its horn at a frequency of 400 Hz. Another car Q is travelling behind the first car in the same direction with a velocity 40 m s^{- 1} . The frequency heard by the passenger of the car Q is approximately [Take, velocity of sound = 360 m s^{- 1}]$ (1) $421 Hz$ (2) $471 Hz$ (3) $485 Hz$ (4) $514 Hz$ 212. $The fundamental frequency of a closed organ pipe is equal to the first overtone frequency of an open organ pipe. If length of the open pipe is 60 cm, the length of the closed pipe will be$ (1) $60 cm$ (2) $45 cm$ (3) $30 cm$ (4) $15 cm$ 213. $A stationary point source of sound emits sound uniformly in all directions in a non absorbing medium. Two points P and Q are at a distance of 4 m and 9 m respectively from the source. The ratio of amplitudes of the waves at P and Q is$ (1) $3/2$ (2) $4/9$ (3) $2/3$ (4) $9/4 .$ 214. $Two sources of sound S_{1} and S_{2} produce sound waves of same frequency 660 Hz . A listener is moving from source S_{1} towards S_{2} with a constant speed u m / s and he hears 10 beats / s . The velocity of sound is 330 m / s . Then u equals:$ (1) $5.5 m / s$ (2) $15.0 m / s$ (3) $2.5 m / s$ (4) $10.0 m / s$ 215. $Two trains move towards each other with the same speed. Speed of sound is 340 m s^{-1} . If the pitch of the tone of the whistle of one when heard on the other changes by 9/8 times, then the speed of each train is:$ (1) $2 m s^{-1}$ (2) $40 m s^{-1}$ (3) $20 m s^{-1}$ (4) $100 m s^{-1}$ 216. $An engine driver moving towards a wall with velocity of 50 m s^{-1} emits a note of frequency 1.2 kHz. The frequency of note after reflection from the wall as heard by the engine driver when speed of sound in air is 350 m s^{-1} is:$ (1) $1 kHz$ (2) $1.8 kHz$ (3) $1.6 kHz$ (4) $1.2 kHz$ 217. $A police car with a siren of frequency 8 kHz is moving with uniform velocity 36 km/hr towards a tall building which reflects the sound waves. The speed of sound in air is 320 m/s. The frequency of the siren heard by the car driver is$ (1) $8.50 kHz$ (2) $8.25 kHz$ (3) $7.75 kHz$ (4) $7.50 kHz$ 218. $A cylindrical tube open at both the ends has a fundamental frequency of 390 Hz in air. If 1/ 4^{th} of the tube is immersed vertically in water the fundamental frequency of air column is$ (1) $260 Hz$ (2) $130 Hz$ (3) $390 Hz$ (4) $520 Hz .$ 219. $A string is vibrating in its fifth overtone between two rigid supports 2.4 m apart. The distance between successive node and antinode is$ (1) $0.1 m$ (2) $0.2 m$ (3) $0.6 m$ (4) $0.8 m$ 220. $Two sound sources each emitting sound of wavelength λ are fixed some distance apart. A listener moves with a velocity u along the line joining the two sources. The number of beats heard by him per second is$ (1) $\frac{2 u}{λ}$ (2) $\frac{u}{λ}$ (3) $\frac{u}{3 λ}$ (4) $0$ 221. $Source and observer both start moving simultaneously from origin, one along X-axis and the other along Y-axis with speed of source equal to twice the speed of observer. The graph between the apparent frequency (n') observed by observer and time t would be: (n is the frequency of the source)$ (1) (2) (3) (4) 222. $In a resonance tube experiment when the tube is filled with water up to a height of 17.0 cm frombottom, it resonates with a given tuning fork. When the water level is raised the next resonance with the same tuning fork occurs at a height of 24.5 cm . If the velocity of sound in air is 330 m / s, the tuning fork frequency is$ (1) $2200 Hz$ (2) $3300 Hz$ (3) $1100 Hz$ (4) $550 Hz$ 223. $A sound source S is moving along a straight track with speed v, and is emitting sound of frequency v_{0} (see figure). An observer is standing at a finite distance, at the point 0, from the track. The time variation of frequency heard by the observer is best represented by (t_{0} represents the instant when the distance between the source and observer is minimum)$ (1) (2) (3) (4) 224. $A whistle revolves in a circle with angular speed co = 20 rad / s using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer which is far away from the centre (velocity of sound = 340 m / s)$ (1) $385 Hz$ (2) $374 Hz$ (3) $394 Hz$ (4) $333 Hz.$ 225. $A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 m s^{-1} at an angle of 60° with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air 330 m s^{-1}) is:$ (1) $103 Hz$ (2) $106 Hz$ (3) $97 Hz$ (4) $100 Hz$ 226. $A student performed the experiment to measure the speed of sound in air using resonance air-column method. Two resonances in the air-column were obtained by lowering the water level. The resonance with the shorter air-column is the first resonance and that with the longer air-column is the second resonance. Then,$ (1) $the intensity of the sound heard at the first resonance was more than that at the second resonance$ (2) $the prongs of the tuning fork were kept in a horizontal plane above the resonance tube$ (3) $the amplitude of vibration of the ends of the prongs is typically around 1 cm$ (4) $the length of the air-column at the first resonance was somewhat shorter than 1/4th of the wavelength of the sound in air.$ 227. $A motor car blowing a horn of frequency 124vib/sec moves with a velocity 72 km/hr towards a tall wall. The frequency of the reflected sound heard by the driver will be (velocity of sound in air is 330 m/s)$ (1) $109 vib/sec$ (2) $132 vib/sec$ (3) $140 vib/sec$ (4) $248 vib/sec$ 228. $A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of19.4 m s^{- 1} at an angle of 6 0^{o} with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air 330 m s^{- 1}), is$ (1) $106 Hz$ (2) $97 Hz$ (3) $100 Hz$ (4) $103 Hz$ 229. $A tuning fork with frequency 800 Hz produces resonance in a resonance column tube with upper end open and lower end closed by water surface. Successive resonance are observed at length 9.75 cm, 31.25 cm and 52.75 cm. The speed of sound in air is [NEET 2019]$ (1) $500 m / s$ (2) $156 m / s$ (3) $344 m / s$ (4) $172 m / s$ 230. $A stationary observer receives sound from two identical tuning forks, one of which approaches and the other one recedes with the same speed (much less than the speed of sound). The observer hears 2 beats/sec. The oscillation frequency of each tuning fork is v_{0} = 1400 Hz and the velocity of sound in air is 350 m/s. The speed of each tuning fork is close to:$ (1) $\frac{1}{4} m / s$ (2) $\frac{1}{2} m / s$ (3) $1 m/s$ (4) $\frac{1}{8} m / s$ 231. $When two tuning forks A and B are sounded together, 4 beats per second are heard. The frequency of the fork B is 384 Hz . When one of the prongs of the fork A is filed and sounded with B, the beat frequency increases, then the frequency of the fork A is$ (1) $388 Hz$ (2) $389 Hz$ (3) $380 Hz$ (4) $379 Hz$ 232. $A speeding motorcyclist sees traffic jam ahead of him. He slows down to 36km/hour. He finds that traffic has eased and a car moving ahead of him at 18 km/hour is honking at a frequency of 1392 Hz. If the speed of sound is 343 m/s, the frequency of the horn as heard by him will be:$ (1) $1332 Hz$ (2) $1372 Hz$ (3) $1412 Hz$ (4) $1454 Hz$ 233. $Source and observer both starts moving simultaneously from origin, one along X-axis and the other along Y-axis with speed of source equal to twice the speed of observer. The graph between the apparent frequency (n') observed by observer and time t would be: (n is the frequency of the source)$ (1) (2) (3) (4) 234. $When both source and listener are approaching each other the observed frequency of sound is given by (V_{L} and V_{S} is the velocity of listener and source respectively, n_{0} = radiated frequency)$ (1) $n = n_{0} (\frac{V + V _{L}}{V - V _{S}})$ (2) $n = n_{0} (\frac{V - V _{L}}{V + V _{S}})$ (3) $n = n_{0} (\frac{V - V _{L}}{V - V _{S}})$ (4) $n = n_{0} (\frac{V + V _{L}}{V + V _{S}})$ 235. $An observer is riding on a bicycle and moving towards a hill at 18 kmh"^{1} . He hears a sound from a source at some distance behind him directly as well as after its reflection from the hill. If the original frequency of the sound as emitted by source is 640 Hz and velocity of the sound in air is 320 m/s, the beat frequency between the two sounds heard by observer will be_____ Hz.$ 236. $A tuning fork is vibrating at 250Hz. The length of the shortest closed organ pipe that will resonate with the tuning fork will be ..... cm. (Take speed of sound in air as 340 m s^{- 1})$ 237. $A closed organ pipe 150 cm long gives 7 beats per second with an open organ pipe of length 350 cm, both vibrating in fundamental mode. The velocity of sound is_______m / s .$ 238. $Two trains move towards each other with the same speed. Speed of sound is 340 m s^{-1} . If the pitch of the tone of the whistle of one when heard on the other changes to 9/8 times, then the speed of each train is:$ 239. $Two cars X and Y are approaching each other with velocities 36km/h and 72km/h respectively. The frequency of a whistle sound as emitted by a passenger in car X, heard by the passenger in car Y is 1320Hz. If the velocity of sound in air is 340m/s, the actual frequency of the whistle sound produced is \dots..Hz$ 240. $A stationary source emits sound of frequency f_{0} = 492 Hz. The sound is reflected by a large car approaching the source with a speed of 2 m s^{-1} . The reflected signal is received by the source and superposed with the original. What will be the beat frequency of the resulting signal in Hz? (Given that the speed of sound in air is 330 m s^{-1} and the car reflects the sound at the frequency it has received)$