Solved papers for JEE Main & Advanced Physics Wave Mechanics JEE PYQ-Wave Mechanics

done JEE PYQ-Wave Mechanics Total Questions - 74

• question_answer1) Tube A has both ends open while tube B has one end closed, otherwise they are identical. The ratio of fundamental frequency of tubes A and B is                                                                           [AIEEE 2002]

A)
$1:2$

B)
$1:4$

C)
$2:1$

D)
$4:1$

• question_answer2) A tuning fork arrangement (pair) produces 4 beats/s with one fork of frequency 288 cps. A little wax is placed on the unknown fork and it then produces 2 beats/s. The frequency of the unknown fork is                             [AIEEE 2002]

A)
286 cps

B)
292 cps

C)
294 cps

D)
288 cps

• question_answer3) A wave $y=a\sin \,(\omega t-kx)$ on a string meets with another wave producing a node at $x=0$. Then, the equation of the unknown wave is                                   [AIEEE 2002]

A)
$y=a\sin \,(\omega \,t+kx)$

B)
$y=-a\sin \,(\omega \,t+kx)$

C)
$y=a\sin \,(\omega \,t-kx)$

D)
$y=-a\sin \,(\omega \,t-kx)$

• question_answer4) Length of a string tied to two rigid supports is 40 cm. Maximum length (wavelength in cm) of a stationary wave produced on it, is                                                                                                          [AIEEE 2002]

A)
20

B)
80

C)
40

D)
120

• question_answer5) When temperature increases, the frequency of a tuning fork                         [AIEEE 2002]

A)
increases

B)
decreases

C)
remains same

D)
increases or decreases depending on the material

• question_answer6)  The displacement y of a wave travelling in the x-direction is given by $y={{10}^{-4}}\sin \left( 600\,t-2x+\frac{\pi }{3} \right)$ metre where, $x$ is expressed in metres and t in seconds. The speed of the wave motion, in $m{{s}^{-1}}$ is                     [AIEEE 2003]

A)
300

B)
600

C)
1200

D)
200

• question_answer7) A metal wire of linear mass density of $9.8$ g/m is stretched with a tension of 10 kg-wt between two rigid supports 1 m apart. The wire passes at its middle point between the poles of a permanent magnet and it vibrates in resonance when carrying an alternating current of frequency n. The frequency n of the alternating source is                [AIEEE 2003]

A)
50 Hz

B)
100 Hz

C)
200 Hz

D)
25 Hz

• question_answer8) A tuning fork of known frequency 256 Hz makes 5 beats/s with the vibrating string of a piano. The beat frequency decreases to 2 beats/s when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was                                                                                                       [AIEEE 2003]

A)
(256 + 2) Hz

B)
(256 - 2) Hz

C)
(256 - 5) Hz

D)
(256 + 5) Hz

• question_answer9) A particle at the end of a spring executes simple harmonic motion with a period${{t}_{1}},$while the corresponding period for another spring is${{t}_{2}}$. If the period of oscillation with the two springs in series is T, then [AIEEE 2004]

A)
$T={{t}_{1}}+{{t}_{2}}$

B)
${{T}^{2}}=t_{1}^{2}+t_{2}^{2}$

C)
${{T}^{-1}}=t_{1}^{-1}+t_{2}^{-1}$

D)
${{T}^{-2}}=t_{2}^{-2}+t_{2}^{-2}$

• question_answer10) The displacement y of a particle in a medium can be expressed as $y={{10}^{-6}}\sin \left( 100t+20x+\frac{\pi }{4} \right)m$, where t is in second and $x$in metre. The speed of the wave is                                           [AIEEE 2004]

A)
$2000\,m/s$

B)
$5\,\,m/s$

C)
$20\,\,m/s$

D)
$5\pi \,\,m/s$

• question_answer11) When two tuning forks (fork 1 and fork 2) are sounded simultaneously, 4 beats/s are heard. Now, some tape is attached on the prong of the fork 2. When the tuning forks are sounded again, 6 beats/s are heard. If the frequency of fork 1 is 200 Hz, then what was the original frequency of fork 2?                     [AIEEE 2005]

A)
200 Hz

B)
202 Hz

C)
196 Hz

D)
204 Hz

• question_answer12)   An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?                      [AIEEE 2005]

A)
Zero

B)
0.5%

C)
5%

D)
20%

• question_answer13) A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed$v\text{ }m{{s}^{-1}}$. The velocity of sound in air is$300\tilde{\ }m{{s}^{-1}}$. If the person can hear frequencies up to a  maximum of 10000 Hz, the maximum value of v upto which he can hear the whistle is           [AIEEE 2006]

A)
$15\sqrt{2}m{{s}^{-1}}$

B)
$15/\sqrt{2}m{{s}^{-1}}$

C)
$15m{{s}^{-1}}$

D)
$30\,m{{s}^{-1}}$

• question_answer14) A string is stretched between fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. Then, the lowest resonant frequency for this string is                                                                                                                                                      [AIEEE 2006]

A)
105 Hz

B)
1.05 Hz

C)
1050 Hz

D)
10.5 Hz

• question_answer15)  A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of  [AIEEE 2007]

A)
1000

B)
10000

C)
10

D)
100

• question_answer16) The speed of sound in oxygen $({{O}_{2}})$ at a certain temperature is 460 $m{{s}^{-1}}$. The speed of sound in helium (He) at the same temperature will be (assume both gases to be ideal)  [AIEEE 2008]

A)
650 $m{{s}^{-1}}$

B)
330 $m{{s}^{-1}}$

C)
460 $m{{s}^{-1}}$

D)
500 $m{{s}^{-1}}$

• question_answer17) A wave travelling along the x-axis is described by the equation $y\left( x,\,t \right)=0.005\cos \left( \alpha x-\beta t \right)$. If the wavelength and the time period of the wave are 0.08 m and 2.0 s, respectively, then $\alpha$ and $\beta$ in appropriate units are        [AIEEE 2008]

A)
$\alpha =\frac{0.04}{\pi },\,\beta =\frac{1.0}{\pi }$

B)
$\alpha =12.50\pi ,\,\beta =\frac{\pi }{2.0}$

C)
$\alpha =25.00\pi ,\,\beta =\pi$

D)
$\alpha =\frac{0.08}{\pi },\,\beta =\frac{2.0}{\pi }$

• question_answer18) 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                                                      [AIEEE 2008]

A)
$54>x>36$

B) C) D) • question_answer19) A motor cycle starts from rest and accelerates along a straight path at At the straight point of the motor cycle there is a stationary electric siren. How far has the motor cycle gone when the driver hears the frequency of the siren at 94% of its value when the motor cycle was at rest?                                                                                     [AIEEE 2009] (Speed of wound )

A)
49 m

B)
98 m

C)
147 m

D)
196 m

• question_answer20) Three sound waves of equal amplitudes have frequencies They superpose to give beats. The number of beats produced per second will be                                                                                                [AIEEE 2009]

A)
4

B)
3

C)
2

D)
1

• question_answer21)  The equation of a wave on a string of linear mass density is given by (m) The tension in the string is -                                                                                               [AIEEE 2010]

A)
6.25 N

B)
4.0 N

C)
12.5 N

D)
0.5 N

• question_answer22)  The transverse displacement of a wave on a string is given by This represents a                                                                                                    [AIEEE 2011]

A)
Standing wave of frequency B)
Wave moving in direction with speed C)
Wave moving in direction with speed D)
Standing wave of frequency • question_answer23)  A travelling wave represented by is superimposed on another wave represented by The resultant is :                                                                                                 [AIEEE 11-05-2011]

A)
A wave travelling along + x direction

B)
A wave travelling along - x direction

C)
A standing wave having nodes at ..

D)
A standing wave having nodes at • question_answer24) Statement-1 :Two longitudinal waves given by equations: and will have equal intensity. Statement-2 : Intensity of waves of given frequency in same medium is proportional to square of amplitude only. [AIEEE 11-05-2011]

A)
Statement-1 is true, Statement-2 is false.

B)
Statement-1 is true, Statement-2 is true, Statement-2 is the correct explanation of statment-1

C)
Statement-1 is true, Statement-2 is true, Statement-2 is not the correct explanation of Statement-1

D)
Statement-1 is false, Statement-2 is true.

• question_answer25) A cylindrical tube, open at both ends, has a fundamental frequency, f, in air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air-column is now:                                  [AIEEE 2012]

A) B) C) D) • question_answer26) Following are expressions for four plane simple harmonic waves                                [JEE ONLINE 07-05-2012] (i) (ii (iii) (iv) The pairs of waves which will produce destructive interference and stationary waves respectively in a medium, are

A)
(iii, iv), (i, ii)

B)
(i, iii), (ii, iv)

C)
(i, iv),(ii, iii)

D)
(i, ii), (iii, iv)

• question_answer27)  This question has Statement land Statement 2.                                           [JEE ONLINE 07-05-2012] Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement-1: In the resonance tube experiment, if the tuning fork is replaced by another identical turning fork but with its arm having been filled, the length of the air column should be increased to obtain resonance again. Statement-2: On filling the arms, the frequency of a tuning fork increases.

A)
Statement 1 is true. Statement 2 is true, Statement 2 is a correct explanation of Statement 1.

B)
Statement 1 is true, Statement 2 is false.

C)
Statement 1 is false, Statement 2 is true.

D)
Statement 1 is true, Statement 2 is true, and Statement 2 is not a correct explanation of Statement 1.

• question_answer28)  This question has Statement 1 and Statement 2.                                                     [JEE ONLINE 12-05-2012] Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement 1: Bats emitting ultrasonic waves can detect the location of a prey by hearing the waves reflected from it. Statement 2: When the source and the detector are moving, the frequency of reflected waves is changed.

A)
Statement 1 is false. Statement 2 is true.

B)
Statement 1 is true, Statement 2 is false.

C)
Statement 1 is true. Statement 2 is true, Statement 2 is not the correct explanation of Statement 1.

D)
Statement 1 is true. Statement 2 is true, Statement 2 is the correct explanation of Statement 1.

• question_answer29) A wave represented by the equation is superimposed with another wave to form a stationary wave such that the point x  0 is node. The equation for the other wave is                            [JEE ONLINE 12-05-2012]

A) B) C) D) • question_answer30) A uniform tube of length 60.5 cm is held vertically with its lower end dipped in water. A sound source of frequency 500 Hz sends sound waves into the tube. When the length of tube above water is 16 cm and again when it is 50 cm, the tube resonates with the source of sound. Two lowest frequencies (in Hz), to which tube will resonate when it is taken out of water, are (approximately).                                                                                      [JEE ONLINE 19-05-2012]

A)
281, 562

B)
281, 843

C)
276, 552

D)
272, 544

• question_answer31) An air column in a pipe, which is closed at one end, will be in resonance with a vibrating tuning fork of frequency 264 Hz if the length of the column in cm is (velocity of sound = 330 m/s)             [JEE ONLINE 26-05-2012]

A)
125.00

B)
93.75

C)
62.50

D)
187.50

• question_answer32) The disturbance y (x, t) of a wave propagating in the positive x-direction is given by at time t = 0 and by at t = 2 s, where x and y are in meters. The shape of the wave disturbance does not change during the propagation. The velocity of wave in m/s is                                                            [JEE ONLINE 26-05-2012]

A)
2.0

B)
4.0

C)
0.5

D)
1.0

• question_answer33) A sonometer wire of length 1.5 m is made of steel. The tension in it produce an elastic strain of 1%. What is the fundamental frequency of steel if density and elasticity of steel are and  respectively?                                                                                                         [JEE MAIN 2013]

A)
188.5 Hz

B)
178.2 Hz

C)
200.5 Hz

D)
770 Hz

• question_answer34)  When two sound waves travel in the same direction in a medium, the displacements of a particle located at   at time t is given by:  Where and are in meters and t in seconds. The speed of sound in the medium is:  [JEE ONLINE 09-04-2013]

A)
92 m/s

B)
200 m/s

C)
100 m/s

D)
332 m/s

• question_answer35) An engine approaches a hill with a constant speed. When it is a distance of 0.9 km it blows a whistle whose echo is heard by the driver after 5 seconds. If the speed of sound in air is 330 m/s, then the speed of the engine is:                                       [JEE ONLINE 09-04-2013]

A)
32 m/s

B)
27.5 m/s

C)
60 m/s

D)
30 m/s

• question_answer36) A and B are two sources generating sound waves. A listener is situated at C. The frequency of the source at A is 500 Hz A, now, moves towards C with a speed 4 m/s. The number of beats heard at C is 6. When A moves away from C with speed 4 m/s, the number of beats heard at C is 18. The speed of sound is 340 m/s. The frequency of the source at B is:          [JEE ONLINE 22-04-2013] A)
500 Hz

B)
506 Hz

C)
512 Hz

D)
494 Hz

• question_answer37) A sonometer wire of length 114 cm is fixed at both the ends. Where should the two bridges be placed so as to divide the wire into three segments whose fundamental frequencies are in the ratio 1 : 3 : 4?     [JEE ONLINE 23-04-2013]

A)
At 36 cm and 84 cm from one end

B)
At 24 cm and 72 cm from one end

C)
At 48 cm and 96 cm form one end

D)
At 72 cm and 96 cm from one end

• question_answer38) In a transverse wave the distance between a crest and neighboring trough at the same instant is 4.0 cm the distance between a crest and trough at the same place is 1.0 cm. The next crest appears at the same palace after a time interval of The maximum speed of the vibrating particle the medium is:                   [JEE ONLINE 25-04-2013]

A) B) C) D) cm/s

• question_answer39)  A transverse wave is represented by For what value of the wavelength the wave velocity is twice the maximum particle velocity? [JEE ONLINE 09-04-2014]

A)
40 cm

B)
20 cm

C)
10 cm

D)
60 cm

• question_answer40) Two factories are sounding their sirens at 800 Hz. A man goes from one factory to other at a speed of 2m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be:     [JEE ONLINE 11-04-2014]

A)
2

B)
4

C)
8

D)
10

• question_answer41) A source of sound A emitting waves of frequency 1800 Hz is falling towards ground with a terminal speed v. The observer B on the ground directly beneath the source receives waves of frequency 2150 Hz. The source A receives waves, reflected from ground of frequency nearly: (Speed of sound  = 343 m/s)                             [JEE ONLINE 12-04-2014]

A)
2150 Hz

B)
2500 Hz

C)
1800 Hz

D)
2400 Hz

• question_answer42) The total length of a sonometer wire between fixed ends is 110 cm. Two bridges are placed to divide the length of wire in ratio 6 : 3 : 2. The tension in the wire is 400 N and the mass per unit length is 0.01 kg/m. What is the minimum common frequency with which three parts can vibrate?                                           [JEE ONLINE 19-04-2014]

A)
1100 Hz

B)
1000 Hz

C)
166 Hz

D)
100 Hz

• question_answer43) A train is moving on a straight track with speed . It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound ) close to                                                                                          [JEE MAIN 2015]

A)
18%

B)
24%

C)
6%

D)
12%

• question_answer44) A bat moving at towards a wall sends a sound signal of 8000 Hz towards it. On reflection it hears a sound of frequency f. The value of f in Hz is dose to (speed of sound )                    [JEE ONLINE 10-04-2015]

A)
8516

B)
8000

C)
8424

D)
8258

 A source of sound emits sound waves at frequency It is moving towards an observer with fixed speed where is the speed of sound in air). If the observer were to move towards the source with speed one of the following two graphs (A and B) will give the correct variation of the frequency f heard by the observer as is changed. [JEE MAIN 11-04-2015] The variation of f with is given correctly by:

A)
graph A with slope B)
graph A with slope C)
graph B with slope D)
graph B with slope • question_answer46) A uniform string of length 20m is suspended from a rigid support. A short wave pulse is introduced at its lowest end. It starts moving up the string. The time taken to reach the support is:                        [JEE MAIN - I 3-4-2016] (take )

A) B) C) D) • question_answer47) A pipe open at both ends has a fundamental frequency f in air. The pipe is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now:-                           [JEE MAIN - I 3-4-2016]

A)
f

B) C) D)
2f

• question_answer48) Two engines pass each other moving in opposite directions with uniform speed of 30m/s. One of them is blowing a whistle of frequency 540 Hz. Calculate the frequency heard by driver of second engine before pass each other. Speed sound is 330 m/sec.                                                                                                                         [JEE ONLINE 09-04-2016]

A)
540 Hz

B)
648 Hz

C)
270 Hz

D)
450 Hz

• question_answer49) A toy-car, blowing its horn, is moving with a steady speed of 5 m/s, away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beat per second. If the velocity of sound in air is 340 m/s, the frequency of horn of the toy car is close to:                                                                                     [JEE ONLINE 10-04-2016]

A)
340Hz

B)
170 Hz

C)
510 Hz

D)
680 Hz

• question_answer50)  Two wires and have the same radius r and respective densities and such that They are joined together at the point O, as shown in the figure. The combination is used as a sonometer wire and kept under tension T. The point O is midway between the two bridges. When a stationary waves is set up in the composite wire, the joint is found to be a node. The ratio of the number of antinodes formed in to is  [JEE Online 08-04-2017]

A)
4 : 1

B)
1 : 2

C)
1 : 1

D)
1 : 3

• question_answer51)  A standing wave is formed by the superposition of two waves travelling in opposite directions. The transverse displacement is given by What is the speed of the travelling wave moving in the positive x direction? (x and t are in meter and second, respectively.)       [JEE Online 09-04-2017]

A)
120 m/s

B)
90 m/s

C)
160 m/s

D)
180 m/s

• question_answer52) A granite rod of 60 cm length is clamped at its middle point and is set into longitudinal vibrations. The density of granite is $2.7\times {{10}^{3}}\text{ }kg/{{m}^{3}}$ and its Young's modulus is$\text{9}\text{.27}\times \text{1}{{\text{0}}^{\text{10}}}\text{ Pa}$. What will be the fundamental frequency of the longitudinal vibrations?                                                                                      [JEE Main Online 08-04-2018]

A)
$10\,\,kHz$

B)
$7.5\,\,kHz$

C)
$5\,\,kHz$

D)
$2.5\,\,kHz$

• question_answer53) A tuning fork vibrates with frequency $256Hz$and gives one best per second with the third normal mode of vibration of an open pipe. What is the length of the pipe? (Speed of sound of air is $340m{{s}^{-1}}$)       [JEE Online 15-04-2018]

A)
$190cm$

B)
$180cm$

C)
$220cm$

D)
$200cm$

• question_answer54) 5 beats/ second are heard when a turning fork is sounded with a sonometer wire under tension, when the length of the sonometer wire is either $0.95m$ or $1m$. The frequency of the fork will be:                      [JEE Online 15-04-2018 (II)]

A)
$195Hz$

B)
$251Hz$

C)
$150Hz$

D)
$300Hz$

• question_answer55) The end correction of a resonance column is $1\,cm$If the shortest length resonating with the tuning fork is$10\,cm,$the next resonating length should be                                                                        [JEE Main Online 16-4-2018]

A)
32 cm

B)
40 cm

C)
28 cm

D)
36 cm

• question_answer56) A particle executes simple harmonic motion and is located at$x=a,b$and c at times${{t}_{0}},2{{t}_{0}}$ and$3{{t}_{0}}$respectively. The frequency of the oscillation is                              [JEE Main Online 16-4-2018]

A)
$\frac{1}{2\pi {{t}_{0}}}{{\cos }^{-1}}\left( \frac{a+b}{2c} \right)$

B)
$\frac{1}{2\pi {{t}_{0}}}{{\cos }^{-1}}\left( \frac{a+b}{3c} \right)$

C)
$\frac{1}{2\pi {{t}_{0}}}{{\cos }^{-1}}\left( \frac{2a+3c}{b} \right)$

D)
$\frac{1}{2\pi {{t}_{0}}}{{\cos }^{-1}}\left( \frac{a+c}{2b} \right)$

• question_answer57) Two sitar strings, A and B, playing the note 'Dha' are slightly out of tune and produce beats and frequency $5\,Hz.$ The tension of the string B is slightly increased and the beat frequency is found to decrease by$3\,Hz.$If the frequency of is , the original frequency of A is 425 Hz, the original frequency of B is

A)
430 Hz

B)
428 Hz

C)
422 Hz

D)
420 Hz

• question_answer58) A heavy ball the mass M is suspended from the ceiling of a car by a right string of mass m $\left( m<<M \right)$. When the car is at rest, the speed of transverse waves in the string is $60\text{ }m{{s}^{-1}}$. When the car has acceleration a, the wave-speed increases to $60.5\text{ }m{{s}^{-1}}$. The value of a, in terms of gravitational acceleration g, is closest to: [JEE Main 09-Jan-2019 Morning]

A)
$\frac{g}{20}$

B)
$\frac{g}{5}$

C)
$\frac{g}{10}$

D)
$\frac{g}{30}$

• question_answer59) A musician using an open flute of length 50 cm produces second harmonic sound waves. A person runs towards the musician from another end of a hall at n speed of 10 km/h. If the wave speed is 330 m/s, the frequency heard by the running person shall be close to:                                                                    [JEE Main 09-Jan-2019 Evening]

A)
753 Hz

B)
666 Hz

C)
500 Hz

D)
333 Hz

• question_answer60) A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is${{f}_{1}}$. If the speed of the train is reduced to 17 m/s, the frequency registered is${{f}_{2}}$. If speed of sound is 340 m/s, then the ratio ${{f}_{1}}/{{f}_{2}}$ is -        [JEE Main 10-Jan-2019 Morning]

A)
19/18

B)
20/19

C)
21/20

D)
18/17

• question_answer61) A string of length 1 m and mass 5 g is fixed at both ends. The tension in the string is 8.0 N. The string is set into vibration using an external vibrator of frequency 100 Hz. The separation between successive nodes on the string is close to-          [JEE Main 10-Jan-2019 Morning]

A)
16.6 cm

B)
10.0 cm

C)
20.0 cm

D)
33.3 cm

• question_answer62) A wire of length 2L, is made by joining two wires A and B of same length but different radii r and 2r and made of the same material. It is vibrating at a frequency such that the joint of the two wires forms a node. If the number of antinodes in wire A is p and that in B is q then the ratio p : q is :                                                 [JEE Main 8-4-2019 Morning] A)
4 : 9

B)
3 : 5

C)
1 : 4

D)
1 : 2

• question_answer63) The pressure wave, $P=0.01$ $\sin \left[ 1000t3x \right]$$N{{m}^{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 $336m{{s}^{-1}}.$Approximate value of T is: [JEE Main 9-4-2019 Morning]

A)
$15{}^\circ C$

B)
$12{}^\circ C$

C)
$4{}^\circ C$

D)
$11{}^\circ C$

• question_answer64) A stationary source emits sound waves of frequency 500 Hz. Two observers moving along a line passing through the source detect sound to be of frequencies 480 Hz and 530 Hz. Their respective speeds are, in $m{{s}^{-1}},$ (Given speed of sound = 300 m/s)                                                            [JEE Main 10-4-2019 Morning]

A)
16, 14

B)
12, 18

C)
12, 16

D)
8, 18

• question_answer65) A source of sound S is moving with a velocity of 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz. What will be the apparent frequency of the source when it is moving away from the observer after crossing him? (Take velocity of sound in air is 350 m/s)                    [JEE Main 10-4-2019 Afternoon]

A)
857 Hz

B)
807 Hz

C)
750 Hz

D)
1143 Hz

• question_answer66)  A progressive wave travelling along the positive x-direction is represented by $y\left( x,\text{ }t \right)=A\sin$$(kx-\omega t+\phi )$. Its snapshot at $t=0$is given in the figure: For this wave, the phase $\phi$is :                                                           [JEE Main Held on 12-4-2019 Morning]

A)
$0$

B)
$-\frac{\pi }{2}$

C)
$\pi$

D)
$\frac{\pi }{2}$

• question_answer67) 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, ${{l}_{1}}=30cm$and ${{l}_{2}}=70cm$. Then n is equal to :                                                                                 [JEE Main 12-4-2019 Afternoon]

A)
$332m{{s}^{-1}}$

B)
$379m{{s}^{-1}}$

C)
$384m{{s}^{-1}}$

D)
$338m{{s}^{-1}}$

• question_answer68) 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: [JEE Main 12-4-2019 Afternoon]

A)
2.5 m/s

B)
15.0 m/s

C)
5.5 m/s

D)
10.0 m/s

• question_answer69) A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect 120 dB intensity sound? [Given reference intensity of sound as ${{10}^{-12}}W/{{m}^{2}}$]    [JEE Main 12-4-2019 Afternoon]

A)
10 cm

B)
30 cm

C)
40 cm

D)
20 cm

• question_answer70) Speed of transverse wave on a straight wire (mass 6.0 g, length 60 cm and area of cross section$1.0\,\,m{{m}^{2}}$) is $90\text{ }m{{s}^{1}}$. If the Youngs modulus of wire is $16\times {{10}^{11}}\text{ }N{{m}^{2}}$, the extension of wire over its natural length is: [JEE MAIN Held on 07-01-2020 Morning]

A)
0.01 mm

B)
0.02 mm

C)
0.04 mm

D)
0.03 mm

• question_answer71) A one meter long (both ends open) organ pipe is kept in a gas that has double the density of air at STP. Assuming the speed of sound in air at STP in 300 m/s, the frequency difference between the fundamental and second harmonic of this pipe is  Hz.                                                                   [JEE MAIN Held On 08-01-2020 Morning]

• question_answer72) A transverse wave travels on a taut steel wire with a velocity of v when tension in it is$2.06\times \,\,{{10}^{4}}\text{ }N.$ When the tension is changed to T, the velocity changed to v/2. The value of T is close to            [JEE MAIN Held on 08-01-2020 Evening]

A)
$30.5\times {{10}^{4}}\text{ }N$

B)
$2.50\times {{10}^{4}}\text{ }N$

C)
$5.15\times {{10}^{3}}\text{ }N$

D)
$10.2\times {{10}^{2}}\text{ }N$

• question_answer73) Three harmonic waves having equal frequency $\nu$and same intensity${{I}_{0}}$, have phase angles $0,\frac{\pi }{4}$ and $-\frac{\pi }{4}$ respectively. When they are superimposed the intensity of the resultant wave is close to  [JEE MAIN Held on 09-01-2020 Morning]

A)
$3{{I}_{0}}$

B)
$~5.8{{I}_{0}}$

C)
$0.2{{I}_{0}}$

D)
${{I}_{0}}$

• question_answer74) A wire of length L and mass per unit length $6.0\times {{10}^{3}}\text{ }kg\text{ }{{m}^{1}}$ is put under tension of 540 N. Two consecutive frequencies that it resonates at are: 420 Hz and 490 Hz. Then L in meters is [JEE MAIN Held on 09-01-2020 Evening]

A)
1.1 m

B)
5.1 m

C)
8.1 m

D)
2.1 m

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