DC Pandey Solutions (JEE Advance): Sound Waves | DC Pandey Solutions for JEE Physics PDF Download

 Page 1


For JEE Advanced 
Objective Questions 
  Single Correct Option 
Q 1.  A plane wave of sound travelling in air is incident upon a plane water surface. The angle of 
incidence is 60°. If velocity of sound in air and water are 330 m/s and 1400 m/s, then the wave 
undergoes 
  (a) refraction only     (b) reflection only 
  (c) Both reflection and refraction   (d) neither reflection nor refraction 
Q 2.  An organ pipe of 3.9 % m long, open at both ends is driven to third harmonic standing wave. If the 
amplitude of pressure oscillation is 1% of mean atmospheric pressure [p0 = 10
5
 N/m
2
 ]. The 
maximum displacement of particle from mean position will be 
  [Given velocity of sound = 200 m/s and density of air = 1.3 kg/m
3
 ] 
  (a) 2.5 cm   (b) 5 cm   (c) 1 cm   (d) 2 cm 
Q 3.  A plane sound wave passes from medium 1 into medium 2. The speed of sound in medium 1 is 
200 m/s and in medium 2 is 100 m/s. The ratio of amplitude of the transmitted wave to that of 
incident wave is 
 (a) 
3
4
   (b) 
4
5
    (c) 
5
6
    (d) 
2
3
 
Q 4.  Two sources of sound are moving in opposite directions with velocities v1 and v2 (v1 > v2). Both 
are moving away from a stationary observer. The frequency of both the sources is 1700 Hz. What 
is the value of (v1 - v 2) so that the beat frequency observed by the observer is 10 Hz? vsound = 340 
m/s and assume that v1 and v2 both are very much less than vsomd. 
  (a) 1 m/s   (b) 2 m/s   (c) 3 m/s   (d) 4 m/s 
Q 5.  A sounding body emitting a frequency of 150 Hz is dropped from a height. During its fall under 
gravity it crosses a balloon moving upwards with a constant velocity of 2 m/s one second after it 
started to fall. The difference in the frequency observed by the man in balloon just before and just 
after crossing the body will be (velocity of sound = 300 m/s, g = 10 m/s
2
) 
  (a) 12    (b) 6    (c) 8    (d) 4 
Q 6.  A closed organ pipe has length L. The air in it is vibrating in third overtone with maximum 
amplitude a. The amplitude at distance 
L
7
 
from closed end of the pipe is 
  (a) 0    (b) a    (c) 
a
2
    (d) Data insufficient 
Q 7.  S1 and S2 are two coherent sources of sound having no initial phase difference. The velocity of 
sound is 330 m/s. No maxima will be formed on the line passing through S2 and perpendicular to 
the line joining S1 and S2- If the frequency of both the sources is 
Page 2


For JEE Advanced 
Objective Questions 
  Single Correct Option 
Q 1.  A plane wave of sound travelling in air is incident upon a plane water surface. The angle of 
incidence is 60°. If velocity of sound in air and water are 330 m/s and 1400 m/s, then the wave 
undergoes 
  (a) refraction only     (b) reflection only 
  (c) Both reflection and refraction   (d) neither reflection nor refraction 
Q 2.  An organ pipe of 3.9 % m long, open at both ends is driven to third harmonic standing wave. If the 
amplitude of pressure oscillation is 1% of mean atmospheric pressure [p0 = 10
5
 N/m
2
 ]. The 
maximum displacement of particle from mean position will be 
  [Given velocity of sound = 200 m/s and density of air = 1.3 kg/m
3
 ] 
  (a) 2.5 cm   (b) 5 cm   (c) 1 cm   (d) 2 cm 
Q 3.  A plane sound wave passes from medium 1 into medium 2. The speed of sound in medium 1 is 
200 m/s and in medium 2 is 100 m/s. The ratio of amplitude of the transmitted wave to that of 
incident wave is 
 (a) 
3
4
   (b) 
4
5
    (c) 
5
6
    (d) 
2
3
 
Q 4.  Two sources of sound are moving in opposite directions with velocities v1 and v2 (v1 > v2). Both 
are moving away from a stationary observer. The frequency of both the sources is 1700 Hz. What 
is the value of (v1 - v 2) so that the beat frequency observed by the observer is 10 Hz? vsound = 340 
m/s and assume that v1 and v2 both are very much less than vsomd. 
  (a) 1 m/s   (b) 2 m/s   (c) 3 m/s   (d) 4 m/s 
Q 5.  A sounding body emitting a frequency of 150 Hz is dropped from a height. During its fall under 
gravity it crosses a balloon moving upwards with a constant velocity of 2 m/s one second after it 
started to fall. The difference in the frequency observed by the man in balloon just before and just 
after crossing the body will be (velocity of sound = 300 m/s, g = 10 m/s
2
) 
  (a) 12    (b) 6    (c) 8    (d) 4 
Q 6.  A closed organ pipe has length L. The air in it is vibrating in third overtone with maximum 
amplitude a. The amplitude at distance 
L
7
 
from closed end of the pipe is 
  (a) 0    (b) a    (c) 
a
2
    (d) Data insufficient 
Q 7.  S1 and S2 are two coherent sources of sound having no initial phase difference. The velocity of 
sound is 330 m/s. No maxima will be formed on the line passing through S2 and perpendicular to 
the line joining S1 and S2- If the frequency of both the sources is 
 
   (a) 330 Hz   (b) 120 Hz   (c) 100 Hz   (d) 220 Hz 
Q 8.  A source is moving with constant speed v s = 20m/s towards a stationary observer due east of the 
source. 
Wind is blowing at the speed of 20 m/s at 60° north of east. The source has frequency 500 Hz. 
Speed of sound = 300m/s. The frequency registered by the observer is approximately 
  (a) 541.Hz   (b) 552 Hz   (c) 534 Hz   (d) 517 Hz 
Q 9.  A car travelling towards a hill at 10 m/s sounds its horn which has a frequency 500 Hz. This is 
heard in a second car travelling behind the first car in the same direction with speed 20 m/s. The 
sound can also be heard in the second car by reflection of sound from the hill. The beat frequency 
heard by the driver of the second car will be (speed of sound in air = 340 m/s) 
  (a) 31 Hz   (b) 24 Hz   (c) 21 Hz   (d) 34 Hz 
Q 10.  Two sounding bodies are producing progressive waves given by y 1 = 2 sin (400 ?t) and y 2 = sin 
(404 ?t) where t is in second, which superpose near the ears of a person. The person will hear 
  (a) 2 beats/s with intensity ratio 9/4 between maxima and minima 
  (b) 2 beats/s with intensity ratio 9 between maxima and minima  
(c) 4 beats/s with intensity ratio 16 between maxima and minima 
  (d) 4 beats/s with intensity ratio 16/9 between maxima and minima 
Q 11.  The air in a closed tube 34 cm long is vibrating with two nodes and two antinodes and its 
temperature is 51 °C. What is the wavelength of the waves produced in air outside the tube, when 
the temperature of air is 16°C? 
  (a) 42.8 cm   (b) 68 cm   (c) 17 cm   (d) 102 cm 
Q 12.  A police car moving at 22 m/s, chase a motorcyclist. The police man sounds his horn at 176 Hz, 
while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of 
the motorcyclist, if he does not observe any beats, (velocity of sound in air = 330m/s) 
 
  (a) 33 m/s   (b) 22 m/s   (c) zero   (d) 11 m/s 
Q 13.  A closed organ pipe resonates in its fundamental mode at a frequency of 200 Hz with O 2 in the 
pipe at a certain temperature. If the pipe now contains 2 moles of O 2 and 3 moles of ozone, then 
what will be the fundamental frequency of same pipe at same temperature? 
  (a) 268.23 Hz   (b) 175.4 Hz   (c) 149.45 Hz   (d) None of these 
Page 3


For JEE Advanced 
Objective Questions 
  Single Correct Option 
Q 1.  A plane wave of sound travelling in air is incident upon a plane water surface. The angle of 
incidence is 60°. If velocity of sound in air and water are 330 m/s and 1400 m/s, then the wave 
undergoes 
  (a) refraction only     (b) reflection only 
  (c) Both reflection and refraction   (d) neither reflection nor refraction 
Q 2.  An organ pipe of 3.9 % m long, open at both ends is driven to third harmonic standing wave. If the 
amplitude of pressure oscillation is 1% of mean atmospheric pressure [p0 = 10
5
 N/m
2
 ]. The 
maximum displacement of particle from mean position will be 
  [Given velocity of sound = 200 m/s and density of air = 1.3 kg/m
3
 ] 
  (a) 2.5 cm   (b) 5 cm   (c) 1 cm   (d) 2 cm 
Q 3.  A plane sound wave passes from medium 1 into medium 2. The speed of sound in medium 1 is 
200 m/s and in medium 2 is 100 m/s. The ratio of amplitude of the transmitted wave to that of 
incident wave is 
 (a) 
3
4
   (b) 
4
5
    (c) 
5
6
    (d) 
2
3
 
Q 4.  Two sources of sound are moving in opposite directions with velocities v1 and v2 (v1 > v2). Both 
are moving away from a stationary observer. The frequency of both the sources is 1700 Hz. What 
is the value of (v1 - v 2) so that the beat frequency observed by the observer is 10 Hz? vsound = 340 
m/s and assume that v1 and v2 both are very much less than vsomd. 
  (a) 1 m/s   (b) 2 m/s   (c) 3 m/s   (d) 4 m/s 
Q 5.  A sounding body emitting a frequency of 150 Hz is dropped from a height. During its fall under 
gravity it crosses a balloon moving upwards with a constant velocity of 2 m/s one second after it 
started to fall. The difference in the frequency observed by the man in balloon just before and just 
after crossing the body will be (velocity of sound = 300 m/s, g = 10 m/s
2
) 
  (a) 12    (b) 6    (c) 8    (d) 4 
Q 6.  A closed organ pipe has length L. The air in it is vibrating in third overtone with maximum 
amplitude a. The amplitude at distance 
L
7
 
from closed end of the pipe is 
  (a) 0    (b) a    (c) 
a
2
    (d) Data insufficient 
Q 7.  S1 and S2 are two coherent sources of sound having no initial phase difference. The velocity of 
sound is 330 m/s. No maxima will be formed on the line passing through S2 and perpendicular to 
the line joining S1 and S2- If the frequency of both the sources is 
 
   (a) 330 Hz   (b) 120 Hz   (c) 100 Hz   (d) 220 Hz 
Q 8.  A source is moving with constant speed v s = 20m/s towards a stationary observer due east of the 
source. 
Wind is blowing at the speed of 20 m/s at 60° north of east. The source has frequency 500 Hz. 
Speed of sound = 300m/s. The frequency registered by the observer is approximately 
  (a) 541.Hz   (b) 552 Hz   (c) 534 Hz   (d) 517 Hz 
Q 9.  A car travelling towards a hill at 10 m/s sounds its horn which has a frequency 500 Hz. This is 
heard in a second car travelling behind the first car in the same direction with speed 20 m/s. The 
sound can also be heard in the second car by reflection of sound from the hill. The beat frequency 
heard by the driver of the second car will be (speed of sound in air = 340 m/s) 
  (a) 31 Hz   (b) 24 Hz   (c) 21 Hz   (d) 34 Hz 
Q 10.  Two sounding bodies are producing progressive waves given by y 1 = 2 sin (400 ?t) and y 2 = sin 
(404 ?t) where t is in second, which superpose near the ears of a person. The person will hear 
  (a) 2 beats/s with intensity ratio 9/4 between maxima and minima 
  (b) 2 beats/s with intensity ratio 9 between maxima and minima  
(c) 4 beats/s with intensity ratio 16 between maxima and minima 
  (d) 4 beats/s with intensity ratio 16/9 between maxima and minima 
Q 11.  The air in a closed tube 34 cm long is vibrating with two nodes and two antinodes and its 
temperature is 51 °C. What is the wavelength of the waves produced in air outside the tube, when 
the temperature of air is 16°C? 
  (a) 42.8 cm   (b) 68 cm   (c) 17 cm   (d) 102 cm 
Q 12.  A police car moving at 22 m/s, chase a motorcyclist. The police man sounds his horn at 176 Hz, 
while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of 
the motorcyclist, if he does not observe any beats, (velocity of sound in air = 330m/s) 
 
  (a) 33 m/s   (b) 22 m/s   (c) zero   (d) 11 m/s 
Q 13.  A closed organ pipe resonates in its fundamental mode at a frequency of 200 Hz with O 2 in the 
pipe at a certain temperature. If the pipe now contains 2 moles of O 2 and 3 moles of ozone, then 
what will be the fundamental frequency of same pipe at same temperature? 
  (a) 268.23 Hz   (b) 175.4 Hz   (c) 149.45 Hz   (d) None of these 
Q 14.  A detector is released from rest over a source of sound of frequency f0 = 10
3
 Hz. The frequency 
observed by the detector at time t is plotted in the graph. The speed of sound in air is (g = 10 m/s 
2
 
) 
 
  (a) 330 m/s   (b) 350 m/s   (c) 300 m/s   (d) 310 m/s 
  Passage : (Q. No. 15 to 17) 
A man of mass 50 kg is running on a plank of mass 150 kg with speed of 8 m/s relative to plank as 
shown in the figure (both were initially at rest and the velocity of man with respect to ground any 
how remains constant). Plank is placed on smooth horizontal surface. The man, while running 
whistles with frequency fo. A detector (D) placed on plank detects frequency. The man jumps off 
with same velocity (w.r.t. to ground) from point D and slides on the smooth horizontal surface 
[Assume coefficient of friction between man and horizontal is zero]. The speed of sound in still 
medium is 330 m/s. Answer following questions on the basis of above situations. 
 
Q 15.  The frequency of sound detected by detector D, before man jumps off the plank is 
 (a) 
0
332
f
324
   (b) 
0
330
f
322
   (c) 
0
328
f
336
   (d) 
0
330
f
338
 
Q 16.  The frequency of sound detected by detector D, after man jumps off the plank is 
 (a) 
0
332
f
324
   (b) 
0
330
f
322
   (c) 
0
328
f
336
   (d) 
0
330
f
338
 
Q 17.  Choose the correct plot between the frequency detected by detector versus position of the man 
 relative to detector 
  (a)    (b) 
  (c)    (d) 
Page 4


For JEE Advanced 
Objective Questions 
  Single Correct Option 
Q 1.  A plane wave of sound travelling in air is incident upon a plane water surface. The angle of 
incidence is 60°. If velocity of sound in air and water are 330 m/s and 1400 m/s, then the wave 
undergoes 
  (a) refraction only     (b) reflection only 
  (c) Both reflection and refraction   (d) neither reflection nor refraction 
Q 2.  An organ pipe of 3.9 % m long, open at both ends is driven to third harmonic standing wave. If the 
amplitude of pressure oscillation is 1% of mean atmospheric pressure [p0 = 10
5
 N/m
2
 ]. The 
maximum displacement of particle from mean position will be 
  [Given velocity of sound = 200 m/s and density of air = 1.3 kg/m
3
 ] 
  (a) 2.5 cm   (b) 5 cm   (c) 1 cm   (d) 2 cm 
Q 3.  A plane sound wave passes from medium 1 into medium 2. The speed of sound in medium 1 is 
200 m/s and in medium 2 is 100 m/s. The ratio of amplitude of the transmitted wave to that of 
incident wave is 
 (a) 
3
4
   (b) 
4
5
    (c) 
5
6
    (d) 
2
3
 
Q 4.  Two sources of sound are moving in opposite directions with velocities v1 and v2 (v1 > v2). Both 
are moving away from a stationary observer. The frequency of both the sources is 1700 Hz. What 
is the value of (v1 - v 2) so that the beat frequency observed by the observer is 10 Hz? vsound = 340 
m/s and assume that v1 and v2 both are very much less than vsomd. 
  (a) 1 m/s   (b) 2 m/s   (c) 3 m/s   (d) 4 m/s 
Q 5.  A sounding body emitting a frequency of 150 Hz is dropped from a height. During its fall under 
gravity it crosses a balloon moving upwards with a constant velocity of 2 m/s one second after it 
started to fall. The difference in the frequency observed by the man in balloon just before and just 
after crossing the body will be (velocity of sound = 300 m/s, g = 10 m/s
2
) 
  (a) 12    (b) 6    (c) 8    (d) 4 
Q 6.  A closed organ pipe has length L. The air in it is vibrating in third overtone with maximum 
amplitude a. The amplitude at distance 
L
7
 
from closed end of the pipe is 
  (a) 0    (b) a    (c) 
a
2
    (d) Data insufficient 
Q 7.  S1 and S2 are two coherent sources of sound having no initial phase difference. The velocity of 
sound is 330 m/s. No maxima will be formed on the line passing through S2 and perpendicular to 
the line joining S1 and S2- If the frequency of both the sources is 
 
   (a) 330 Hz   (b) 120 Hz   (c) 100 Hz   (d) 220 Hz 
Q 8.  A source is moving with constant speed v s = 20m/s towards a stationary observer due east of the 
source. 
Wind is blowing at the speed of 20 m/s at 60° north of east. The source has frequency 500 Hz. 
Speed of sound = 300m/s. The frequency registered by the observer is approximately 
  (a) 541.Hz   (b) 552 Hz   (c) 534 Hz   (d) 517 Hz 
Q 9.  A car travelling towards a hill at 10 m/s sounds its horn which has a frequency 500 Hz. This is 
heard in a second car travelling behind the first car in the same direction with speed 20 m/s. The 
sound can also be heard in the second car by reflection of sound from the hill. The beat frequency 
heard by the driver of the second car will be (speed of sound in air = 340 m/s) 
  (a) 31 Hz   (b) 24 Hz   (c) 21 Hz   (d) 34 Hz 
Q 10.  Two sounding bodies are producing progressive waves given by y 1 = 2 sin (400 ?t) and y 2 = sin 
(404 ?t) where t is in second, which superpose near the ears of a person. The person will hear 
  (a) 2 beats/s with intensity ratio 9/4 between maxima and minima 
  (b) 2 beats/s with intensity ratio 9 between maxima and minima  
(c) 4 beats/s with intensity ratio 16 between maxima and minima 
  (d) 4 beats/s with intensity ratio 16/9 between maxima and minima 
Q 11.  The air in a closed tube 34 cm long is vibrating with two nodes and two antinodes and its 
temperature is 51 °C. What is the wavelength of the waves produced in air outside the tube, when 
the temperature of air is 16°C? 
  (a) 42.8 cm   (b) 68 cm   (c) 17 cm   (d) 102 cm 
Q 12.  A police car moving at 22 m/s, chase a motorcyclist. The police man sounds his horn at 176 Hz, 
while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of 
the motorcyclist, if he does not observe any beats, (velocity of sound in air = 330m/s) 
 
  (a) 33 m/s   (b) 22 m/s   (c) zero   (d) 11 m/s 
Q 13.  A closed organ pipe resonates in its fundamental mode at a frequency of 200 Hz with O 2 in the 
pipe at a certain temperature. If the pipe now contains 2 moles of O 2 and 3 moles of ozone, then 
what will be the fundamental frequency of same pipe at same temperature? 
  (a) 268.23 Hz   (b) 175.4 Hz   (c) 149.45 Hz   (d) None of these 
Q 14.  A detector is released from rest over a source of sound of frequency f0 = 10
3
 Hz. The frequency 
observed by the detector at time t is plotted in the graph. The speed of sound in air is (g = 10 m/s 
2
 
) 
 
  (a) 330 m/s   (b) 350 m/s   (c) 300 m/s   (d) 310 m/s 
  Passage : (Q. No. 15 to 17) 
A man of mass 50 kg is running on a plank of mass 150 kg with speed of 8 m/s relative to plank as 
shown in the figure (both were initially at rest and the velocity of man with respect to ground any 
how remains constant). Plank is placed on smooth horizontal surface. The man, while running 
whistles with frequency fo. A detector (D) placed on plank detects frequency. The man jumps off 
with same velocity (w.r.t. to ground) from point D and slides on the smooth horizontal surface 
[Assume coefficient of friction between man and horizontal is zero]. The speed of sound in still 
medium is 330 m/s. Answer following questions on the basis of above situations. 
 
Q 15.  The frequency of sound detected by detector D, before man jumps off the plank is 
 (a) 
0
332
f
324
   (b) 
0
330
f
322
   (c) 
0
328
f
336
   (d) 
0
330
f
338
 
Q 16.  The frequency of sound detected by detector D, after man jumps off the plank is 
 (a) 
0
332
f
324
   (b) 
0
330
f
322
   (c) 
0
328
f
336
   (d) 
0
330
f
338
 
Q 17.  Choose the correct plot between the frequency detected by detector versus position of the man 
 relative to detector 
  (a)    (b) 
  (c)    (d) 
Q 18.  Sound waves are travelling along positive x-direction. Displacement of particle at any time t is as 
shown in figure. Select the wrong statement. 
 
  (a) Particle located at E has its velocity in negative x-direction 
  (b) Particle located at D has zero velocity 
  (c) Both (a) and (b) are correct 
  (d) Both (a) and (b) are wrong 
More than One Correct Options 
Q 19.  An air column in a pipe, which is closed at one end, is in resonance with a vibrating tuning fork of 
frequency 264 Hz. If v = 330 m/s, the length of the column in cm is (are) 
  (a) 31.25   (b) 62.50   (c) 93.75   (d) 125 
Q 20.  Which of the following is/are correct? 
  (a)    (b) 
  (c)    (d) 
Q 21.  Choose the correct options for longitudinal wave 
  (a) maximum pressure variation is B Ak (b) maximum density variation is 
  (c) pressure equation and density equation are in phase 
  (d) pressure equation and displacement equation are out of phase 
Q 22.  Second overtone frequency of a closed pipe and fourth harmonic frequency of an open pipe are 
same. Then choose the correct options. 
  (a) Fundamental frequency of closed pipe is more than the fundamental frequency of open pipe 
  (b) First overtone frequency of closed pipe is more than the first overtone frequency of open pipe 
(c) Fifteenth harmonic frequency of closed pipe is equal to twelfth harmonic frequency of open 
pipe 
  (d) Tenth harmonic frequency of closed pipe is equal to eighth harmonic frequency of open pipe 
Q 23.  For fundamental frequency f of a closed pipe, choose the correct options. 
  (a) If radius of pipe is increased f will decrease  
  (b) If temperature is increased f will increase  
  (c) If molecular mass of the gas filled in the pipe is increased /will decrease. 
Page 5


For JEE Advanced 
Objective Questions 
  Single Correct Option 
Q 1.  A plane wave of sound travelling in air is incident upon a plane water surface. The angle of 
incidence is 60°. If velocity of sound in air and water are 330 m/s and 1400 m/s, then the wave 
undergoes 
  (a) refraction only     (b) reflection only 
  (c) Both reflection and refraction   (d) neither reflection nor refraction 
Q 2.  An organ pipe of 3.9 % m long, open at both ends is driven to third harmonic standing wave. If the 
amplitude of pressure oscillation is 1% of mean atmospheric pressure [p0 = 10
5
 N/m
2
 ]. The 
maximum displacement of particle from mean position will be 
  [Given velocity of sound = 200 m/s and density of air = 1.3 kg/m
3
 ] 
  (a) 2.5 cm   (b) 5 cm   (c) 1 cm   (d) 2 cm 
Q 3.  A plane sound wave passes from medium 1 into medium 2. The speed of sound in medium 1 is 
200 m/s and in medium 2 is 100 m/s. The ratio of amplitude of the transmitted wave to that of 
incident wave is 
 (a) 
3
4
   (b) 
4
5
    (c) 
5
6
    (d) 
2
3
 
Q 4.  Two sources of sound are moving in opposite directions with velocities v1 and v2 (v1 > v2). Both 
are moving away from a stationary observer. The frequency of both the sources is 1700 Hz. What 
is the value of (v1 - v 2) so that the beat frequency observed by the observer is 10 Hz? vsound = 340 
m/s and assume that v1 and v2 both are very much less than vsomd. 
  (a) 1 m/s   (b) 2 m/s   (c) 3 m/s   (d) 4 m/s 
Q 5.  A sounding body emitting a frequency of 150 Hz is dropped from a height. During its fall under 
gravity it crosses a balloon moving upwards with a constant velocity of 2 m/s one second after it 
started to fall. The difference in the frequency observed by the man in balloon just before and just 
after crossing the body will be (velocity of sound = 300 m/s, g = 10 m/s
2
) 
  (a) 12    (b) 6    (c) 8    (d) 4 
Q 6.  A closed organ pipe has length L. The air in it is vibrating in third overtone with maximum 
amplitude a. The amplitude at distance 
L
7
 
from closed end of the pipe is 
  (a) 0    (b) a    (c) 
a
2
    (d) Data insufficient 
Q 7.  S1 and S2 are two coherent sources of sound having no initial phase difference. The velocity of 
sound is 330 m/s. No maxima will be formed on the line passing through S2 and perpendicular to 
the line joining S1 and S2- If the frequency of both the sources is 
 
   (a) 330 Hz   (b) 120 Hz   (c) 100 Hz   (d) 220 Hz 
Q 8.  A source is moving with constant speed v s = 20m/s towards a stationary observer due east of the 
source. 
Wind is blowing at the speed of 20 m/s at 60° north of east. The source has frequency 500 Hz. 
Speed of sound = 300m/s. The frequency registered by the observer is approximately 
  (a) 541.Hz   (b) 552 Hz   (c) 534 Hz   (d) 517 Hz 
Q 9.  A car travelling towards a hill at 10 m/s sounds its horn which has a frequency 500 Hz. This is 
heard in a second car travelling behind the first car in the same direction with speed 20 m/s. The 
sound can also be heard in the second car by reflection of sound from the hill. The beat frequency 
heard by the driver of the second car will be (speed of sound in air = 340 m/s) 
  (a) 31 Hz   (b) 24 Hz   (c) 21 Hz   (d) 34 Hz 
Q 10.  Two sounding bodies are producing progressive waves given by y 1 = 2 sin (400 ?t) and y 2 = sin 
(404 ?t) where t is in second, which superpose near the ears of a person. The person will hear 
  (a) 2 beats/s with intensity ratio 9/4 between maxima and minima 
  (b) 2 beats/s with intensity ratio 9 between maxima and minima  
(c) 4 beats/s with intensity ratio 16 between maxima and minima 
  (d) 4 beats/s with intensity ratio 16/9 between maxima and minima 
Q 11.  The air in a closed tube 34 cm long is vibrating with two nodes and two antinodes and its 
temperature is 51 °C. What is the wavelength of the waves produced in air outside the tube, when 
the temperature of air is 16°C? 
  (a) 42.8 cm   (b) 68 cm   (c) 17 cm   (d) 102 cm 
Q 12.  A police car moving at 22 m/s, chase a motorcyclist. The police man sounds his horn at 176 Hz, 
while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of 
the motorcyclist, if he does not observe any beats, (velocity of sound in air = 330m/s) 
 
  (a) 33 m/s   (b) 22 m/s   (c) zero   (d) 11 m/s 
Q 13.  A closed organ pipe resonates in its fundamental mode at a frequency of 200 Hz with O 2 in the 
pipe at a certain temperature. If the pipe now contains 2 moles of O 2 and 3 moles of ozone, then 
what will be the fundamental frequency of same pipe at same temperature? 
  (a) 268.23 Hz   (b) 175.4 Hz   (c) 149.45 Hz   (d) None of these 
Q 14.  A detector is released from rest over a source of sound of frequency f0 = 10
3
 Hz. The frequency 
observed by the detector at time t is plotted in the graph. The speed of sound in air is (g = 10 m/s 
2
 
) 
 
  (a) 330 m/s   (b) 350 m/s   (c) 300 m/s   (d) 310 m/s 
  Passage : (Q. No. 15 to 17) 
A man of mass 50 kg is running on a plank of mass 150 kg with speed of 8 m/s relative to plank as 
shown in the figure (both were initially at rest and the velocity of man with respect to ground any 
how remains constant). Plank is placed on smooth horizontal surface. The man, while running 
whistles with frequency fo. A detector (D) placed on plank detects frequency. The man jumps off 
with same velocity (w.r.t. to ground) from point D and slides on the smooth horizontal surface 
[Assume coefficient of friction between man and horizontal is zero]. The speed of sound in still 
medium is 330 m/s. Answer following questions on the basis of above situations. 
 
Q 15.  The frequency of sound detected by detector D, before man jumps off the plank is 
 (a) 
0
332
f
324
   (b) 
0
330
f
322
   (c) 
0
328
f
336
   (d) 
0
330
f
338
 
Q 16.  The frequency of sound detected by detector D, after man jumps off the plank is 
 (a) 
0
332
f
324
   (b) 
0
330
f
322
   (c) 
0
328
f
336
   (d) 
0
330
f
338
 
Q 17.  Choose the correct plot between the frequency detected by detector versus position of the man 
 relative to detector 
  (a)    (b) 
  (c)    (d) 
Q 18.  Sound waves are travelling along positive x-direction. Displacement of particle at any time t is as 
shown in figure. Select the wrong statement. 
 
  (a) Particle located at E has its velocity in negative x-direction 
  (b) Particle located at D has zero velocity 
  (c) Both (a) and (b) are correct 
  (d) Both (a) and (b) are wrong 
More than One Correct Options 
Q 19.  An air column in a pipe, which is closed at one end, is in resonance with a vibrating tuning fork of 
frequency 264 Hz. If v = 330 m/s, the length of the column in cm is (are) 
  (a) 31.25   (b) 62.50   (c) 93.75   (d) 125 
Q 20.  Which of the following is/are correct? 
  (a)    (b) 
  (c)    (d) 
Q 21.  Choose the correct options for longitudinal wave 
  (a) maximum pressure variation is B Ak (b) maximum density variation is 
  (c) pressure equation and density equation are in phase 
  (d) pressure equation and displacement equation are out of phase 
Q 22.  Second overtone frequency of a closed pipe and fourth harmonic frequency of an open pipe are 
same. Then choose the correct options. 
  (a) Fundamental frequency of closed pipe is more than the fundamental frequency of open pipe 
  (b) First overtone frequency of closed pipe is more than the first overtone frequency of open pipe 
(c) Fifteenth harmonic frequency of closed pipe is equal to twelfth harmonic frequency of open 
pipe 
  (d) Tenth harmonic frequency of closed pipe is equal to eighth harmonic frequency of open pipe 
Q 23.  For fundamental frequency f of a closed pipe, choose the correct options. 
  (a) If radius of pipe is increased f will decrease  
  (b) If temperature is increased f will increase  
  (c) If molecular mass of the gas filled in the pipe is increased /will decrease. 
(d) If pressure of gas (filled in the pipe) is increased without change in temperature, f will remain 
unchanged 
Q 24.  A source is approaching towards an observer with constant speed along the line joining them. 
After crossing the observer, source recedes from observer with same speed. Let /is apparent 
frequency heard by observer. Then 
  (a) f will increase during approaching  (b) f will decrease during receding 
  (c) f will remain constant during approaching (d) f will remain constant during receding 
Answers 
  1.(b) 2.(a) 3.(d) 4.(b) 5.(a) 6.(b) 7.(c) 8.(c) 9.(a) 10.(b) 11.(a) 12.(b) 13.(b) 14.(c) 15.(a) 16.(c)  
  17.(a) 18.(c) 
More than One Correct Options 
  19. (a,c) 20. (c,d) 21. (a,b,c) 22. (b,c,d) 23. (a,b,c,d) 24. (c,d) 
Solutions 
1.  
   
  Since i > ?C, therefore only reflection will take place. 
2.      ...(i) 
      
  
  
 
    
  Substituting in Eq. (i) we have, 
    
    
   = 0.025 m = 2.5 cm 
3.  
   
4.  fb = f1 - f2