Sound Waves PYQs Set 2 (PDF)

Set 2 of 9 · Questions 31-60 of 268

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Mere Teacher · Previous Year Questions JEE Main Physics · Sound Waves · Set 2 (Q31-60)
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31. $A table is revolving on its axis at 5 revolutions per second. A sound source of frequency 1000 Hz is fixed on the table at 70 cm from the axis. The minimum frequency heard by a listener standing at a distance from the table will be (speed of sound = 352 m/s)$ (1) $1000 Hz$ (2) $1066 Hz$ (3) $941 Hz$ (4) $352 Hz$ 32. $A tuning fork of frequency 480 Hz is used in an experiment for measuring speed of sound (v) in air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column, l_{1} = 30 cm and l_{2} = 70 cm Then, v is equal to:$ (1) $332 ms^{- 1}$ (2) $384 ms^{- 1}$ (3) $338 ms^{- 1}$ (4) $379 ms^{- 1}$ 33. $A whistle revolves in a circle with angular speed ꞷ = 20 rad/sec using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency head by an observer which is far away from the center:- (velocity of sound V_{so u n d} = 340m/s)$ (1) $385 Hz$ (2) $374 Hz$ (3) $394 Hz$ (4) $333 Hz$ 34. $4.0 g of a gas occupies 22.4 1itres at NTP. The specific heat capacity of the gas at constant volume is 5.0 J K^{- 1} mo 1^{- 1} . Ifthe speed of sound in this gas at NTP is 952 m s^{- 1}, then the heat capacity at constant pressure is (Take gas constant R = 8.3 J K^{- 1} mo 1^{- 1})$ (1) $7.0 J K^{- 1} mo 1^{- 1}$ (2) $8.5 J K^{- 1} mo 1^{- 1}$ (3) $8.0 J K^{- 1} mo 1^{- 1}$ (4) $7.5 J K^{- 1} mo 1^{- 1}$ 35. $Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: A sound wave has higher speed in solids than gases. Reason R: Gases have higher value of Bulk modulus than solids. choose the correct answer from the options given below$ (1) $Both A and R are true but R is NOT the correct explanation of A$ (2) $A is true but R is false$ (3) $A is false but R is true$ (4) $Both A and R are true and R is the correct explanation of A$ 36. $The fifth harmonic of a closed organ pipe is found to be in unison with the first harmonic of an open pipe. The ratio of lengths of closed pipe to that of the open pipe is 5/ x . The value of x is____.$ (1) $3$ (2) $4$ (3) $1$ (4) $2$ 37. $When an engine passes near to a stationary observe then its apparent frequencies occurs in the ratio 5/3. If the velocity of sound is 340 m/s then speed of engine is:$ (1) $540 m/s$ (2) $270 m/s$ (3) $85 m/s$ (4) $52.5 m/s$ 38. $The temperature at which the speed of sound becomes double as was at 2 7^{o} C is$ (1) $27 3^{o} C$ (2) $0^{o} C$ (3) $92 7^{o} C$ (4) $102 7^{o} C$ 39. $A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 2 7^{o} C two successive resonances are produced at 20 cm and 73 cm ofcolumn length. If the frequency of the tuning fork is 320 Hz, the velocity of sound in air at 2 7^{o} C is$ (1) $330 m s^{- 1}$ (2) $339 m s^{- 1}$ (3) $350 m s^{- 1}$ (4) $300 m s^{- 1}$ 40. $A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 27ºC two successive resonances are produced at 20 cm and 73 cm of column length. If the frequency of the tuning fork is 320 Hz, the velocity of sound in air at 27ºC is:$ (1) $330 m/s$ (2) $300 m/s$ (3) $350 m/s$ (4) $339 m/s$ 41. $The velocity of sound in a gas. in which two wavelengths 4.08m and 4.16m produce 40 beats in 12s, will be:$ (1) $2.82. 8 m s^{- 1}$ (2) $175. 5 m s^{- 1}$ (3) $353.6 m s^{- 1}$ (4) $707.2 m s^{- 1}$ 42. $Two coherent sources produce waves of different intensities which interfere. After interference, the ratio of the maximum intensity to the minimum intensity is 16 The intensity of the waves are in the ratio:$ (1) $16 : 9$ (2) $25 : 9$ (3) $4 : 1$ (4) $5 : 3$ 43. $The apparent change in the pitch of sound due to relative motion between observer and the source is called-$ (1) $doppler’s effect$ (2) $resonance of waves$ (3) $interference$ (4) $none of the above$ 44. $A source and observer are approaching each other with 50 m s^{-1} velocity. What will be original frequency if the observer receives 400 cycle/s?$ (1) $300 cycle/s$ (2) $320 cycle/s$ (3) $340 cycle/s$ (4) $330 cycle/s$ 45. $A person with vibrating tuning fork of frequency 338 Hz is moving towards a vertical wall with a speed of 2 ms^{- 1} . Velocity of sound in air is 340 m s^{- 1} . The number of beats heard by that person per second is$ (1) $2$ (2) $4$ (3) $6$ (4) $8$ 46. $An observer is moving away from source of sound of frequency 100 Hz. His speed is 33 m/s. If speed of sound is 330 m/s, then the observed frequency is$ (1) $90 Hz$ (2) $100 Hz$ (3) $91 Hz$ (4) $110 Hz$ 47. $A student is performing the experiment of resonance column. The diameter of the column tube is 6 cm . Thefrequency of the tuning fork is 504 Hz . Speed of the sound at the given temperature is 336 m / s . The zero ofthe meter scale coincides with the top end of the resonance column tube. The reading of the water level in the column when the first resonance occurs is:$ (1) $13 cm$ (2) $14.8 cm$ (3) $16.6 cm$ (4) $18.4 cm$ 48. $The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length ofthe open pipe will be$ (1) $L$ (2) $2 L$ (3) $\frac{L}{2}$ (4) $4 L$ 49. $Wave has simple harmonic motion whose period is 4 s econds while another wave which also possesses simple harmonic motion has its period 3 second. If both are combined, then the resultant wave will have the period equal to$ (1) $4 s$ (2) $52$ (3) $12 s$ (4) $3 s$ 50. $A source of unknown frequency gives 4 beats/s when sounded with a source of known frequency 250 Hz. The second harmonic of the source of unknown frequency gives five beats per second, when sounded with a source of frequency 513 Hz. The unknown frequency is$ (1) $240 Hz$ (2) $260 Hz$ (3) $254 Hz$ (4) $246 Hz$ 51. $A source of sound of frequency n is moving towards a stationary observer with a speed S. If the speed of sound in air is V and the frequency heard by the observer is n_{1}, the value of n_{1} / n is$ (1) $(V + S) / V$ (2) $V / (V + S)$ (3) $(V - S) / V$ (4) $V / (V - S)$ 52. $A train whistling at constant frequency n is moving towards a station at a constant speed v . The train goes past a stationary observer on the station. The frequency n of the sound as heard by the observer is plotted as a function of time t . Identify the correct curve.$ (1) (2) (3) (4) 53. $When source of sound moves towards a stationary observer, the wavelength of sound received by him$ (1) $decreases while frequency increases.$ (2) $remains the same whereas frequency increases.$ (3) $increases and frequency also increases.$ (4) $decreases while frequency remains the same.$ 54. $The driver of a car travelling with speed 30 m / s towards a hill sounds a horn offrequency 600 Hz. If the velocity of sound in air is 330 m / s, the frequency ofreflected sound as heard by driver is$ (1) $555.5 Hz$ (2) $720 Hz$ (3) $500 Hz$ (4) $550 Hz$ 55. $Two open pipes of different lengths and of same diameter in which the air column vibrates with fundamental frequencies ' n_{1}' and ' n_{2}' respectively. When both pipes are joined to form a single pipe, its fundamental frequency will be$ (1) $\frac{n _{1} + n _{2}}{n _{1} n _{2}}$ (2) $\frac{n _{1} n _{2}}{2 n _{2} + n _{1}}$ (3) $\frac{2 n _{2} + n _{1}}{n _{1} n _{2}}$ (4) $\frac{n _{1} n _{2}}{n _{1} + n _{2}}$ 56. $Two identical strings X and Z made of same material have tension T_{x} and T_{z} in them. If their fundamental frequencies are 450 Hz and 300 Hz respectively, then the ratio T_{x} / T_{z} is$ (1) $1.5$ (2) $2.25$ (3) $0.44$ (4) $1.25$ 57. $A source of frequency v gives 5 beats/second when sounded with a source offrequency200 Hz. The second harmonic of frequency 2 v of source gives 10 beats/second when sounded with a source of frequency 420 Hz. The value of v is$ (1) $205 Hz$ (2) $195 Hz$ (3) $200 Hz$ (4) $210 Hz.$ 58. $The speed of sound in air at a given temperature is 350 m/s. An engine blows whistle at a frequency of 1200 cps. It is approaching the observer with velocity 50 m/s. The apparent frequency in cps heard by the observer will be$ (1) $600$ (2) $1050$ (3) $1400$ (4) $2400$ 59. $A wire of length 30 cm, stretched between rigid supports, has it's n^{t h} and (n + 1)^{t h} harmonics at 400 Hz and 450 Hz, respectively. If tension in the string is 2700 N, it's linear mass density is........kg/m.$ 60. $A tuning fork of frequency 340 Hz resonates in the fundamental mode with an air column of length 125 cm in a cylindrical tube closed at one end. When water is slowly poured in it, the minimum height of water required for observing resonance once again is______ cm. (Velocity of sound in air is 340 m s^{- 1})$