Sound Waves PYQs Set 7 (PDF)

Set 7 of 9 · Questions 181-210 of 268

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Mere Teacher · Previous Year Questions JEE Main Physics · Sound Waves · Set 7 (Q181-210)
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181. $An observer is moving with half the speed of light towards stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer? (speed of light = 3 \times 10^{8} ms^{- 1})$ (1) $15.3 GHz$ (2) $10.1 GHz$ (3) $12.1 GHz$ (4) $17.3 GHz$ 182. $A tuning fork of frequency 512 Hz makes 4 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per sec when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was$ (1) $510 Hz$ (2) $514 Hz$ (3) $516 Hz$ (4) $508 Hz$ 183. $How many times more intense is a 60 dB sound than a 30 dB sound?$ (1) $100$ (2) $4$ (3) $1000$ (4) $2$ 184. $The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length of the open pipe will be [NEET 2016]$ (1) $L$ (2) $2 L$ (3) $\frac{L}{2}$ (4) $4 L$ 185. $The wavelength is 120 cm when the source is stationary. If the source is moving with relative velocity of 60 m/sec towards the observer, then the wavelength of the sound wave reaching to the observer will be (velocity of sound = 330 m/s)$ (1) $98 cm$ (2) $140 cm$ (3) $120 cm$ (4) $144 cm$ 186. $The observer is moving with velocity v_{0} towards the stationary source of sound and then after crossing moves away from the source with velocity v_{0} . Assume that the medium through which the sound waves travel is at rest. If v is the velocity of sound and n is the frequency emitted by the source then the difference between apparent frequencies heard by the observer is$ (1) $\frac{2 n v _{0}}{v}$ (2) $\frac{n v _{0}}{v}$ (3) $\frac{v}{2 n v _{0}}$ (4) $\frac{v}{n v _{0}}$ 187. $A source of sound is moving towards a stationary observer with (\frac{1}{10})^{th} of the speed of sound. The ratio of apparent to real frequency is$ (1) $10 : 9$ (2) $11 : 10$ (3) $(11)^{2} : (10)^{2}$ (4) $(9)^{2} : (10)^{2}$ 188. $Two factories are sounding their sirens at 400 Hz each. A man walks from one factory towards the other at a speed of 2 m/s. the speed of sound is 320 m/s. The number of beats heard per second by the man is.$ (1) $6$ (2) $5$ (3) $2.5$ (4) $7.5$ 189. $In an open organ pipe ν_{3} and ν_{6} are 3^{rd} and 6^{th} harmonic frequencies, respectively. If ν_{6} - ν_{3} = 2200 Hz then length of the pipe is____mm . (Take velocity of sound in air is 330 m / s .)$ (1) $275$ (2) $250$ (3) $225$ (4) $200$ 190. $An open and closed organ pipe have the same length. The ratio of ' p' th mode of frequency of vibration of air in two pipes is$ (1) $p (2 p + 1)$ (2) $\frac{2 p}{2 p - 1}$ (3) $p$ (4) $1$ 191. $With what speed should a galaxy move outward with respect to earth so that the sodium-D line at wavelength 5890 A \dots is observed at 5896 A \dots?$ (1) $306 km/sec$ (2) $322 km/sec$ (3) $296 km/sec$ (4) $336 km/sec$ 192. $A stationary observer receives sound from two identical tuning forks, one of which approaches and the other one recedes with the same speed (much less than the speed of sound). The observer hears 2 beats / sec . The oscillation frequency of each tuning fork is v_{o} = 1400 Hz and the velocity of sound in air is 350 m / s . The speed of each tuning fork is close to:$ (1) $\frac{1}{4}$ (2) $4$ (3) $2$ (4) $\frac{1}{2}$ 193. $Sound of frequency 1000 Hz from a stationary source is reflected from an object approaching the source at 30 m s^{- 1}, back to a stationary observer located at the source. The speed of sound in air is 330 m s^{- 1} . The frequency of the sound heard by the observer is$ (1) $1200 Hz$ (2) $1000 Hz$ (3) $1090 Hz$ (4) $1100 Hz$ 194. $Suppose that the speed of sound in air at a given temperature is 400 m/sec. An engine blows a whistle at 1200 Hz frequency. It is approaching an observer at the speed of 100 m/sec. What is the apparent frequency as heard by the observer$ (1) $600 Hz$ (2) $1200 Hz$ (3) $1500 Hz$ (4) $1600 Hz$ 195. $A siren emitting sound of frequency 500 Hz is going away from a static listener with a speed of 50 m/sec. The frequency of sound to be heard, directly from the siren, is$ (1) $434.2 Hz$ (2) $589.3 Hz$ (3) $481.2 Hz$ (4) $286.5 Hz$ 196. $A point source emits sound equally in all directions in a non‐absorbing medium. Two points P and Q are at distances of 2 m and 3 m respectively from the source. The ratio of the intensities of the waves at P and Q is$ (1) $3: 2$ (2) $2: 3$ (3) $9: 4$ (4) $4: 9$ 197. $A source of sound gives 5 beats per second, when sounded with another source of frequency 100 secon d^{- 1} . The second harmonic of the source, together with a source of frequency 205 sec^{- 1} gives 5 beats per second. What is the frequency of the source?$ (1) $105 secon d^{- 1}$ (2) $205 secon d^{- 1}$ (3) $95 secon d^{- 1}$ (4) $100 secon d^{- 1}$ 198. $A hollow pipe of length 0.8 m is closed at one end. At its open end a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is 50 N and the speed of sound is 320 ms s^{- 1}, the mass of the string is:$ (1) $5 grams$ (2) $10 grams$ (3) $20 grams$ (4) $40 grams$ 199. $An observer is moving towards the stationary source of sound, then$ (1) $Apparent frequency will be less than the real frequency$ (2) $Apparent frequency will be greater than the real frequency$ (3) $Apparent frequency will be equal to real frequency$ (4) $Only the quality of sound will change$ 200. $A source of sound is travelling with a velocity 40 km/hour towards observer and emits sound of frequency 2000 Hz. If velocity of sound is 1220 km/hour, then what is the apparent frequency heard by an observer$ (1) $2210 Hz$ (2) $1920 Hz$ (3) $2068 Hz$ (4) $2086 Hz$ 201. $An observer standing at station observes frequency 219 Hz when a train approaches and 184 Hz when train goes away from him. If velocity of sound in air is 340 m/s, then velocity of train and actual frequency of whistle will be$ (1) $15.5 m s^{- 1}, 200 Hz$ (2) $19.5 m s^{- 1}, 205 Hz$ (3) $29.5 m s^{- 1}, 200 Hz$ (4) $32.5 m s^{- 1}, 205 Hz$ 202. $Two vehicles, each moving with speed u on the same horizontal straight road, are approaching each other. Wind blows along the road with velocity w. One of these vehicles blows a whistle of frequency f_{1} . An observer in the other vehicle hears the frequency of the whistle to be f_{2} . The speed of sound in still air is V. The correct statement(s) is (are):$ (1) $If the wind blows from the observer to the source, f_{2} > f_{1} .$ (2) $If the wind blows from the source to the observer, f_{2} > f_{1} .$ (3) $If the wind blows from the observer to the source, f_{2} < f_{1} .$ (4) $If the wind blows from the source to the observer, f_{2} < f_{1} .$ 203. $A source of sound S of frequency 500 Hz situated between a stationary observer O and a wall W, moves towards the wall with a speed of 2 m/s. If the velocity of sound is 332 m/s, then the number of beats per second heard by the observer is (approximately)$ (1) $8$ (2) $6$ (3) $4$ (4) $2$ 204. $A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed v ms^{- 1} . The velocity of sound in air is 300 ms^{- 1} . If the person can hear frequencies upto a maximum of 10, 000 Hz, the maximum value of v upto which he can hear the whistle is:$ (1) $30 ms^{- 1}$ (2) $152 ms^{- 1}$ (3) $202 ms-1$ (4) $15 ms^{- 1}$ 205. $In an experiment with a closed organ pipe, it is filled with water by (\frac{1}{5}) th of its volume. The frequency of the fundamental note will change by$ (1) $20 %$ (2) $25 %$ (3) $- 20 %$ (4) $- 25 %$ 206. $As the train crosses a stationary observer, the apparent change in frequency of sound is in the ratio 5 : 3. If velocity of sound in air is 332 m/s, the velocity of train is$ (1) $81 m/s$ (2) $83 m/s$ (3) $90 m/s$ (4) $87 m/s$ 207. $An observer moves on a circle as shown in fig. and a small sound source is at S. Let at v_{1}, v_{2}, v_{3} be the frequencies heard when the observer is at A, B, and C respectively.$ (1) $v_{1} > v_{2} > v_{3}$ (2) $v_{1} = v_{2} > v_{3}$ (3) $v_{2} > v_{3} > v_{1}$ (4) $v_{1} > v_{3} > v_{2}$ 208. $A person standing on an open ground hears the sound of a jet aeroplane, coming from north at an angle 60^{\circ} with ground level. But he finds the aeroplane right vertically above his position. If v is the speed of sound, speed of the plane is:$ (1) $\frac{3}{2} v$ (2) $\frac{2 v}{3}$ (3) $v$ (4) $\frac{v}{2}$ 209. $The frequency of a car horn encountered a change from 400Hz to 500Hz. When the car approaches a vertical wall. If the speed of sound is 330m/s. Then the speed of car is ___ km/h.$ 210. $The frequency of echo will be _________ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h towards a hill from which an echo is heard by the train driver. Velocity of sound in air is 330 m/s.$