Tiêu đề 15. Waves.pdf ✅

1. A car P approaching a crossing at a speed of 10 m/s sounds a horn of frequency 700 Hz when 40 m in front of the crossing. Speed of sound in air is 340 m/s. Another car Q is at rest on a road which is perpendicular to the road on which car P is reaching the crossing (see figure). The driver of car Q hears the sound of the horn of car P when he is 30 m in front of the crossing. The apparent frequency heard by the driver of car Q is (1) 700 Hz (2) 717 Hz (3) 1000 Hz (4) 679 Hz 2. The equation of a wave on a string of linear mass density 0.04 kgm–1 is given by : The tension in the string is : (1) 4.0 N (2) 12.5 N (3) 0.5 N (4) 6.25 N 3. In the standing wave shown, particles at the positions A and B have a phase difference of 4. A closed organ pipe has a frequency 'n'. If its length is doubled and radius is halved, its frequency nearly becomes– (1) halved (2) doubled (3) tripled (4) quadrupled 5 . In a resonance tube experiment, the first resonance is obtained for 10 cm of air column and the second for 32 cm. The end correction for this apparatus is– (1) 0. 5 cm (2) 1. 0 cm (3) 1. 5 cm (4) 2 cm 6. A man is watching two trains, one leaving and the other coming with equal speed of 4m/s. If they sound their whistles each of frequency 240 Hz, the number of beats per sec heard by man will be equal to: (velocity of sound in air= 320 m/s): (1) 12 (2) zero (3) 3 (4) 6 7. Fundamental frequency of a sono meter wire is n. If the length and diameter of the wire are doubled keeping the tension same, then the new fundamental frequency is : 8. An organ pipe P1 closed at one end vibrating in its first overtone and another pipe P2 open at both ends vibrating in its third harmonic are in resonance with a given tuning fork. The ratio of the length of P1 to that of P2is :- (1) 8/3 (2) 1/6 (3) 1/2 (4) 1/3 9. A wave travelling along the x-axis is described by the equation y (x, t ) = 0.005 cos(  x t − ) . If the wavelength and the time period of the wave are 0.08m and 2.0 s respectively then  and  inappropriate units are (1)     = = 25.00 , (2) 0.08 2.0  ,   = = (3) 0.04 1.0  ,   = = (4) 12.50 , 2.0     = = 10. Two waves represented by,y1 = 10sin 200t,y2 = 20sin 200 2 t       +   are superimposed at any point at a particular instant. The amplitude of the resultant wave is : (1) 200 (2) 30 (3) 10 5 (4) 10 3 11. The velocity of sound in air is 330 m/s. The fundamental frequency of an organ pipe open at both ends and of length 0.3 m will be : (1) 200 Hz (2) 550 Hz (3) 330 Hz (4) 275 Hz 12. The amplitude of a wave disturbance propagating in the positive X-direction is given by y = 1/(1 + x2 ) at time t = 0 and by y = 1/[1 + (x – 1)2 ] at t = 2 seconds, where x Waves
and y are in metres. The shape of the wave disturbance does not change during the propagation. The velocity of the wave is (1) 1 ms–1 (2) 0.5 ms–1 (3) 1.5 ms–1 (4) 2 ms–1 13. A uniform rope of mass 6 kg hangs vertically from a rigid support. A block of mass 2 kg is attached to the free end of the rope. A transverse pulse of wavelength 0.06 m is produced at the lower end of the rope. The wavelength of the pulse when it reaches the top is (in m) (1) 0.06 (2) 0.12 (3) 0.03 (4) 0.24 14. When a tuning fork is vibrating, the vibrations of the two prongs (1) Are in phase (2) Differ in phase by 45° (3) Differ in phase by 90° (4) Differ in phase by 180° 15. A stretched string is divided into three segments of lengths 50 cm, 40 cm and 10 cm with the help of bridges. Their vibrations will have frequencies in the ratio (1) 5 : 4 : 1 (2) 1 : 4 : 5 (3) 4 : 5 : 20 (4) 4 : 5 : 10 16. 56 tuning forks are so arranged in increasing order of frequencies in series that each fork gives 4 beats per second with the previous one. The frequency of the last fork is the octave of the first. The frequency of the first fork is (1) 220 Hz (2) 224 Hz (3) (220/7) Hz (4) 110 Hz 17. As a wave propagates :– (1) The wave intensity remains constant for a plane wave (2) The wave intensity decreases as the inverse of the distance from the source for a spherical wave (3) The wave intensity decreases as the inverse of square of the distance from the source for a spherical wave (4) Total intensity of the spherical wave over the spherical surface centred at the source remains constant at all time 18. A vibrating string of certain length under a tension T resonates with a mode corresponding to the first overtone (third harmonic) of an air column of length75 cm inside a tube closed at one end. The string also generates 4 beats per second when excited along with a tuning fork of frequency n. Now when the tension of the string is slightly increased the number of beats reduces to 2 per second. Assuming the velocity of sound in air to be 340 m/s, the frequency n of the tuning fork in Hz is :- (1) 344 (2) 336 (3) 117.3 (4) 109.3 19. A pipe of length 85 cm is closed from one end. Find the number of possible natural oscillations of air column in the pipe whose frequencies lie below 1250 Hz. The velocity of sound in air is 340 m/s. (1) 6 (2) 4 (3) 12 (4) 8 20. Two waves are given by: y1 =cos (4t – 2x) and 2 sin 4 2 4 y t x    = − +     . The phase difference between the two waves is :- 21. A car 'A' chasing another car 'B' with a speed of20 m/s sounding a horn of 180 Hz. While both cars are moving towards a stationary siren of frequency170 Hz. What is the speed of car B so that it can't hear any beat (speed of sound = 340 m/s) (1) 34 m/s (2) 22 m/s (3) 20 m/s (4) zero 22. Two identical flutes produce fundamental notes of frequency 300 Hz at 27°C. If the temperature of air in one flute is increased to 31°C, the number of the beats heard per second will be :- (1) 1 (2) 2 (3) 3 (4) 4 23. A string of mass m and length l hangs from ceiling as shown in the figure. Wave in string moves upward. vA and vB are the speeds of wave at A and B respectively. Then vB is :
(1) 3 A v (2) A v (3) < A v 4) 2 A v 24. When a stone hangs from one end of a sonometer wire of vibrating length 1 it is in resonance with a tuning fork. When the stone hangs wholly immersed in water, the resonant length gets reduced to 2 . The relative density of stone is :- 25. Which of the following statement is false– (1)The wavelength of sound does not depend on reference frame of observer (2)Motion of source of sound effects the wavelength (3) When source of sound and observer both are at rest and medium is moving than wavelength and velocity of sound changes in equal proportion (4)When only medium moves from source to observer, frequency heard by observer will be greater than original frequency 26. The resultant amplitude due to superposition of two waves y1 = 5 sin (t kx − ) and y2 = –5 cos (  t – kx – 150°) is :- (1) 5 (2) 5 3 (3) 5 2 3 − 4) 5 2 3 + 27. A standing wave pattern of amplitude A in a string of length L shows two nodes (plus those at two ends). If one end of the string corresponds to the origin and v is the speed of progressive wave, the disturbance in the string, could be represented (with appropriate phase) as :- 28. The power of sound from the speaker of a radio is 20 mW. By turning the volume control knob the power of sound is increased to 400 mW. The power increase in decibel as compared to the original power is :- (1) 13 dB (2) 10 dB (3) 20 dB (4) 800 dB 29 . 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 50N and the speed of sound is 320 ms–1, the mass of the string is :- (1) 5 grams (2) 10 grams (3) 20 grams (4) 40 grams 30. The amplitude of a wave represented by displacement equation : 1 1 y t t sin cos a b =    will be: (1) a b ab + (2) a b ab + (3) a b ab − (4) a b ab + 31. The frequency of a tuning fork is 256 Hz. The velocity of sound in air is 344 ms–1 . The distance travelled (in meters) by the sound during the time in which the tunning fork complete 32 vibrations is : (1) 21 (2) 43 (3) 86 (4) 1291 32. An engine is moving towards a wall with a velocity 50 ms–1 emits a note of 1.2 kHz. The
speed of sound in air is 350 ms–1 . The frequency of the note after reflection from the wall as heard by the driver of the engine is : (1) 2.4 kHz (2) 0.24 kHz (3) 1.6 kHz (4) 1.2 kHz 33. A sound absorber attenuates (decreases) the sound level by 20 dB. The intensity decreases by a factor of : (1) 100 (2) 1000 (3) 10000 (4) 10 34. In a string the speed of wave is 10 m/s and its frequency is 100 Hz . The value of the phase difference between two points separated by 2.5 cm in radian will be : (1) /2 (2) /8 (3) 32 (4) 2 35. In a resonance tube the first resonance with a tuning fork occurs at 16 cm and second at 49cm. If the velocity of sound is 330 m/s, the frequency of tuning fork is : (1) 500Hz (2) 300 Hz (3) 330 Hz (4) 165 Hz 36. When a guitar string is sounded with a 440 Hz tuning fork a beat frequency of 5 Hz is heard. If the experiment is repeated with a tuning fork of 437 Hz, the beat frequency is 8 Hz. The string frequency (Hz) is – (1) 445 (2) 435 (3) 429 (4) 448 37. A car is moving towards a high cliff. The car driver sounds a horn of frequency ‘f’. The reflected sound heard by the driver has a frequency 2f. If ‘v’ be the velocity of sound then the velocity of the car, in the same velocity units, will be : 38. A wave in a string has amplitude of 2cm. The wave travels in the + ve direction of x axis with a speed of 128 m/s and it is noted that 5 complete waves fit in 4 m length of the string. The equation describing the wave is : (1) y = (0.02) m sin (7.85x – 1005t) (2) y = (0.02) m sin (7.85x + 1005t) (3) y = (0.02) m sin (15.7x – 2010t) (4) y = (0.02)m sin (15.7x + 2010t) 39. Waves from two sources superimpose on each other at a particular point. Amplitude and frequency of both the waves are equal. The ratio of intensities when both waves reach in the same phase and they reach with the phase difference of 90 will be (1) 1:1 (2) 1 : 2 (3) 2:1 (4) 4:1 40. A wave represented by the equation y = a sin(kx – t) is superimposed with another wave to form a stationary wave such that the point x = 0 is a node. Then the equation of other wave is – (1) y = a cos (kx – t) (2) y = acos (kx + t) (3) y = – asin (kx + t) (4) y = a sin (kx + t) 41. A transverse sinusoidal wave moves along a string in the positive x-direction at a speed of 10 cm/s. The wavelength of the wave is 0. 5 m and its amplitude is 10 cm. At a particular time t, the snap shot of the wave is shown in figure. The velocity of P when its displacement is 5 cm is : 42. A set of 56 tuning forks are so arranged in series that each fork gives 4 beats per second with the previous one. The frequency of the last fork is 3 times that of first. The frequency of first fork is : (1) 110 Hz (2) 60 Hz (3) 56 Hz (4) 65 Hz 43. A whistle revolves in a circle with angular speed  = 20 rad/sec using a string of length 50 cm. If t he frequency of sound from t he whistle is 385 Hz, then what is the minimum frequency heard by an observer which is far away from the centre: (V sound == 340 m/s) (1) 385 Hz (2) 374 Hz (3) 394 Hz (4) 333 Hz 44. A cylindrical tube (L = 120 cm) is resonant with a tuning fork of frequency 330 Hz. If it is filled with water, then to get resonance minimum length of water column is (Vair = 330m/s) (1) 45 cm (2) 60 cm (3) 25 cm (4) 20 cm