Sound Waves PYQs Set 6 (PDF)

Set 6 of 8 · Questions 151-180 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Sound Waves · Set 6 (Q151-180)
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151. $A man is watching two trains, one leaving and the other coming in with equal speeds of 4 m/sec. If they sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air = 320 m/sec) will be equal to$ (1) $6$ (2) $3$ (3) $0$ (4) $12$ 152. $A sound source is moving towards a stationary observer with 1/10 of the speed of sound. The ratio of apparent to real frequency is$ (1) $10/9$ (2) $11/10$ (3) $(11/10)^{2}$ (4) $(9/10)^{2}$ 153. $The correct figure that shows, schematically, the wave pattern produced by superposition of two waves of frequencies 9 Hz and 11 Hz is:$ (1) (2) (3) (4) 154. $A police car horn emits a sound at a frequency 240 Hz. when the car is at rest. If the speed of the sound is 330 m/s the frequency heard by an observer who is approaching the car at a speed of 11 m/s, is:$ (1) $248 Hz$ (2) $244 Hz$ (3) $240 Hz$ (4) $230 Hz$ 155. $Which of the following does not affect the apparent frequency in doppler effect?$ (1) $Speed of source$ (2) $Speed of observer$ (3) $Frequency of source$ (4) $Distance between source and observer$ 156. $A train moving with 20 m/s towards a stationary observer produces frequency of 440 Hz. The apparent frequency heard will be (v = 330 m/s)$ (1) $448 Hz$ (2) $455 Hz$ (3) $440 Hz$ (4) $468 Hz$ 157. $The pressure wave P = 0.01 sin [1000 t - 3 x] Nm^{- 2} corresponds to the sound produced by a vibrating blade on a day when atmospheric temperature is 0^{\circ} C . On some other day when temperature is T the speed of sound produced by the same blade and at the same frequency is found to be 336 ms^{- 1} . Approximate value of T is:$ (1) $4^{\circ} C$ (2) $11^{\circ} C$ (3) $12^{\circ} C$ (4) $15^{\circ} C$ 158. $A source of sound of frequency 450 cycles/sec is moving towards a stationary observer with 34 m/sec speed. If the speed of sound is 340 m/sec, then the apparent frequency will be$ (1) $410 cycles/sec$ (2) $500 cycles/sec$ (3) $550 cycles/sec$ (4) $450 cycles/sec$ 159. $While measuring the speed of sound by performing a resonance column experiment, a student gets the first resonance condition at a column length of 18 cm during winter. Repeating the same experiment during summer, she measures the column length to be x cm for the second resonance. Then$ (1) $x > 54$ (2) $54 > x > 36$ (3) $36 > x > 18$ (4) $18 > x$ 160. $Intensity level of sound whose intensity is 10^{- 8} Wm^{- 2} is ... dB$ (1) $8$ (2) $4$ (3) $40$ (4) $80$ 161. $A plane sound wave travelling with velocity v in a medium A reaches a point on the interface of medium A and medium B . If velocity of sound in medium B is 2 v, the angle of incidence for total internal reflection of the wave will be greater than (sin 30^{\circ} = 0.5) and sin 90^{\circ} = 1)$ (1) $15^{\circ}$ (2) $30^{\circ}$ (3) $45^{\circ}$ (4) $90^{\circ}$ 162. $An observer is moving with half the speed of light towards stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer? (speed of light = 3 \times 10^{8} ms^{- 1})$ (1) $15.3 GHz$ (2) $10.1 GHz$ (3) $12.1 GHz$ (4) $17.3 GHz$ 163. $A tuning fork of frequency 512 Hz makes 4 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per sec when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was$ (1) $510 Hz$ (2) $514 Hz$ (3) $516 Hz$ (4) $508 Hz$ 164. $How many times more intense is a 60 dB sound than a 30 dB sound?$ (1) $100$ (2) $4$ (3) $1000$ (4) $2$ 165. $The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length of the open pipe will be [NEET 2016]$ (1) $L$ (2) $2 L$ (3) $\frac{L}{2}$ (4) $4 L$ 166. $The wavelength is 120 cm when the source is stationary. If the source is moving with relative velocity of 60 m/sec towards the observer, then the wavelength of the sound wave reaching to the observer will be (velocity of sound = 330 m/s)$ (1) $98 cm$ (2) $140 cm$ (3) $120 cm$ (4) $144 cm$ 167. $The observer is moving with velocity v_{0} towards the stationary source of sound and then after crossing moves away from the source with velocity v_{0} . Assume that the medium through which the sound waves travel is at rest. If v is the velocity of sound and n is the frequency emitted by the source then the difference between apparent frequencies heard by the observer is$ (1) $\frac{2 n v _{0}}{v}$ (2) $\frac{n v _{0}}{v}$ (3) $\frac{v}{2 n v _{0}}$ (4) $\frac{v}{n v _{0}}$ 168. $A source of sound is moving towards a stationary observer with (\frac{1}{10})^{th} of the speed of sound. The ratio of apparent to real frequency is$ (1) $10 : 9$ (2) $11 : 10$ (3) $(11)^{2} : (10)^{2}$ (4) $(9)^{2} : (10)^{2}$ 169. $Two factories are sounding their sirens at 400 Hz each. A man walks from one factory towards the other at a speed of 2 m/s. the speed of sound is 320 m/s. The number of beats heard per second by the man is.$ (1) $6$ (2) $5$ (3) $2.5$ (4) $7.5$ 170. $In an open organ pipe ν_{3} and ν_{6} are 3^{rd} and 6^{th} harmonic frequencies, respectively. If ν_{6} - ν_{3} = 2200 Hz then length of the pipe is____mm . (Take velocity of sound in air is 330 m / s .)$ (1) $275$ (2) $250$ (3) $225$ (4) $200$ 171. $An open and closed organ pipe have the same length. The ratio of ' p' th mode of frequency of vibration of air in two pipes is$ (1) $p (2 p + 1)$ (2) $\frac{2 p}{2 p - 1}$ (3) $p$ (4) $1$ 172. $With what speed should a galaxy move outward with respect to earth so that the sodium-D line at wavelength 5890 A \dots is observed at 5896 A \dots?$ (1) $306 km/sec$ (2) $322 km/sec$ (3) $296 km/sec$ (4) $336 km/sec$ 173. $A stationary observer receives sound from two identical tuning forks, one of which approaches and the other one recedes with the same speed (much less than the speed of sound). The observer hears 2 beats / sec . The oscillation frequency of each tuning fork is v_{o} = 1400 Hz and the velocity of sound in air is 350 m / s . The speed of each tuning fork is close to:$ (1) $\frac{1}{4}$ (2) $4$ (3) $2$ (4) $\frac{1}{2}$ 174. $Sound of frequency 1000 Hz from a stationary source is reflected from an object approaching the source at 30 m s^{- 1}, back to a stationary observer located at the source. The speed of sound in air is 330 m s^{- 1} . The frequency of the sound heard by the observer is$ (1) $1200 Hz$ (2) $1000 Hz$ (3) $1090 Hz$ (4) $1100 Hz$ 175. $Suppose that the speed of sound in air at a given temperature is 400 m/sec. An engine blows a whistle at 1200 Hz frequency. It is approaching an observer at the speed of 100 m/sec. What is the apparent frequency as heard by the observer$ (1) $600 Hz$ (2) $1200 Hz$ (3) $1500 Hz$ (4) $1600 Hz$ 176. $A siren emitting sound of frequency 500 Hz is going away from a static listener with a speed of 50 m/sec. The frequency of sound to be heard, directly from the siren, is$ (1) $434.2 Hz$ (2) $589.3 Hz$ (3) $481.2 Hz$ (4) $286.5 Hz$ 177. $A point source emits sound equally in all directions in a non‐absorbing medium. Two points P and Q are at distances of 2 m and 3 m respectively from the source. The ratio of the intensities of the waves at P and Q is$ (1) $3: 2$ (2) $2: 3$ (3) $9: 4$ (4) $4: 9$ 178. $A source of sound gives 5 beats per second, when sounded with another source of frequency 100 secon d^{- 1} . The second harmonic of the source, together with a source of frequency 205 sec^{- 1} gives 5 beats per second. What is the frequency of the source?$ (1) $105 secon d^{- 1}$ (2) $205 secon d^{- 1}$ (3) $95 secon d^{- 1}$ (4) $100 secon d^{- 1}$ 179. $A hollow pipe of length 0.8 m is closed at one end. At its open end a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is 50 N and the speed of sound is 320 ms s^{- 1}, the mass of the string is:$ (1) $5 grams$ (2) $10 grams$ (3) $20 grams$ (4) $40 grams$ 180. $An observer is moving towards the stationary source of sound, then$ (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) $Only the quality of sound will change$