JEE Main & Advanced Physics Wave Mechanics Question Bank

done Doppler's Effect Total Questions - 65

• question_answer1)
  Doppler shift in frequency does not depend upon [MP PMT 1993; DPMT 2000]
  A)
             The frequency of the wave produced done clear
  B)
             The velocity of the source done clear
  C)
             The velocity of the observer done clear
  D)
             Distance from the source to the listener done clear
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• question_answer2)
  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                                           [MP PMT 1987]
  A)
             410 cycles/sec                       done clear
  B)
             500 cycles/sec done clear
  C)
             550 cycles/sec                       done clear
  D)
             450 cycles/sec done clear
  View Solution play_arrow

• question_answer3)
  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)
  A)
             98 cm                                       done clear
  B)
             140 cm done clear
  C)
             120 cm                                     done clear
  D)
             144 cm done clear
  View Solution play_arrow

• question_answer4)
  The frequency of a whistle of an engine is 600 cycles/sec is moving with the speed of 30 m/sec towards an observer. The apparent frequency will be (velocity of sound = 330 m/s)                                                     [MP PMT 1989]
  A)
             600 cps                                    done clear
  B)
             660 cps done clear
  C)
             990 cps                                    done clear
  D)
             330 cps done clear
  View Solution play_arrow

• question_answer5)
  A source of sound emits waves with frequency f  Hz and speed V m/sec. Two observers move away from this source in opposite directions each with a speed 0.2 V relative to the source. The ratio of frequencies heard by the two observers will be                                                        [MP PET 1990]
  A)
             3 : 2                                           done clear
  B)
             2 : 3 done clear
  C)
             1 : 1                                           done clear
  D)
             4 : 10 done clear
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• question_answer6)
  The source producing sound and an observer both are moving along the direction of propagation of sound waves. If the respective velocities of sound, source and an observer are v, \[{{v}_{s}}\]and \[{{v}_{o}}\], then the apparent  frequency heard by the observer will be (n = frequency of sound) [MP PMT 1989]
  A)
             \[\frac{n(v+{{v}_{o}})}{v-{{v}_{o}}}\]                             done clear
  B)
             \[\frac{n(v-{{v}_{o}})}{v-{{v}_{s}}}\] done clear
  C)
             \[\frac{n(v-{{v}_{o}})}{v+{{v}_{s}}}\]                             done clear
  D)
             \[\frac{n(v+{{v}_{o}})}{v+{{v}_{s}}}\] done clear
  View Solution play_arrow

• question_answer7)
  An observer moves towards a stationary source of sound of frequency n. The apparent frequency heard by him is 2n. If the velocity of sound in air is 332 m/sec, then the velocity of the observer is                                    [MP PET 1990]
  A)
             166 m/sec                               done clear
  B)
             664 m/sec done clear
  C)
             332 m/sec                               done clear
  D)
             1328 m/sec done clear
  View Solution play_arrow

• question_answer8)
  An observer is moving towards the stationary source of sound, then                                      [MH CET 2001]
  A)
             Apparent frequency will be less than the real frequency done clear
  B)
             Apparent frequency will be greater than the real frequency done clear
  C)
             Apparent frequency will be equal to real frequency done clear
  D)
             Only the quality of sound will change done clear
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• question_answer9)
  A whistle sends out 256 waves in a second. If the whistle approaches the observer with velocity 1/3 of the velocity of sound in air, the number of waves per second the observer will receive                [MP PET 1990; DPMT 2002]
  A)
             384 done clear
  B)
             192 done clear
  C)
             300 done clear
  D)
             200 done clear
  View Solution play_arrow

• question_answer10)
  A person feels 2.5% difference of frequency of a motor-car horn. If the motor-car is moving to the person and the velocity of sound is 320 m/sec, then the velocity of car will be                     [CPMT 1981; MP PET 1989]
  A)
             8 m/s (approx.)                    done clear
  B)
             800 m/s done clear
  C)
             7 m/s                                        done clear
  D)
             6 m/s (approx.) done clear
  View Solution play_arrow

• question_answer11)
  Two passenger trains moving with a speed of 108 km/hour cross each other. One of them blows a whistle whose frequency is 750 Hz. If sound speed is 330 m/s, then passengers sitting in the other train, after trains cross each other will hear sound whose frequency will be        [MP PMT 1991]
  A)
             900 Hz                                      done clear
  B)
             625 Hz done clear
  C)
             750 Hz                                      done clear
  D)
             800 Hz done clear
  View Solution play_arrow

• question_answer12)
  With what velocity an observer should move relative to a stationary source so that he hears a sound of double the frequency of source                                                [MP PMT 1991]
  A)
             Velocity of sound towards the source done clear
  B)
             Velocity of sound away from the source done clear
  C)
             Half the velocity of sound towards the source done clear
  D)
             Double the velocity of sound towards the source done clear
  View Solution play_arrow

• question_answer13)
  A source of sound emitting a note of frequency 200 Hz moves towards an observer with a velocity v equal to the velocity of sound. If the observer also moves away from the source with the same velocity v, the apparent frequency heard by the observer is                     [MP PMT 1990]
  A)
             50 Hz                                        done clear
  B)
             100 Hz done clear
  C)
             150 Hz                                      done clear
  D)
             200 Hz done clear
  View Solution play_arrow

• question_answer14)
  Doppler's effect will not be applicable when the velocity of sound source is
  A)
             Equal to that of the sound velocity done clear
  B)
             Less than the velocity of sound done clear
  C)
             Greater than the velocity of sound done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer15)
  An observer while going on scooter hears sound of two sirens of same frequencies from two opposite directions. If he travels along the direction of one of the siren, then he
  A)
             Listens resonance done clear
  B)
             Listens beats done clear
  C)
             Will not listen sound due to destructive interference done clear
  D)
             Will listen intensive sound due to constructive interference done clear
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• question_answer16)
  A source of sound is travelling towards a stationary observer. The frequency of sound heard by the observer is of three times the original frequency. The velocity of sound is v m/sec. The speed of source will be [MP PET 1991]
  A)
             \[\frac{2}{3}v\]                    done clear
  B)
             v done clear
  C)
             \[\frac{3}{2}v\]                    done clear
  D)
             3v done clear
  View Solution play_arrow

• question_answer17)
  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                       [CPMT 1977; NCERT 1977; KCET 2001, 03]
  A)
             10/9                                          done clear
  B)
             11/10 done clear
  C)
             \[{{(11/10)}^{2}}\]              done clear
  D)
             \[{{(9/10)}^{2}}\] done clear
  View Solution play_arrow

• question_answer18)
  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 [CPMT 1976; RPET 1999; BHU 1997, 2001]
  A)
             600 done clear
  B)
             1050 done clear
  C)
             1400                                          done clear
  D)
             2400 done clear
  View Solution play_arrow

• question_answer19)
  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                                            [CPMT 1983; DPMT 2001]
  A)
             600 Hz                                      done clear
  B)
             1200 Hz done clear
  C)
             1500 Hz                                    done clear
  D)
             1600 Hz done clear
  View Solution play_arrow

• question_answer20)
  A source of frequency 150 Hz is moving in the direction of a person with a velocity of 110 m/s. The frequency heard by the person will be (speed of sound in medium = 330 m/s)                            [CPMT 1989; RPET 2001]
  A)
             225 Hz                                      done clear
  B)
             200 Hz done clear
  C)
             150 Hz                                      done clear
  D)
             100 Hz done clear
  View Solution play_arrow

• question_answer21)
  The Doppler's effect is applicable for                  [AFMC 1998]
  A)
             Light waves                           done clear
  B)
             Sound waves done clear
  C)
             Space waves                         done clear
  D)
             Both (a) and (b) done clear
  View Solution play_arrow

• question_answer22)
  A source of sound is moving with constant velocity of 20 m/s emitting a note of frequency 1000 Hz. The ratio of frequencies observed by a stationary observer while the source is approaching him and after it crosses him will be [MP PET 1994]
  A)
             9 : 8                                           done clear
  B)
             8 : 9 done clear
  C)
             1 : 1                                           done clear
  D)
             9 : 10 (Speed of sound v = 340 m/s) done clear
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• question_answer23)
  A source of sound S is moving with a velocity 50m/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 ? The velocity of sound in the medium is 350 m/s                                             [MP PMT 1994]
  A)
             750 Hz                                      done clear
  B)
             857 Hz done clear
  C)
             1143 Hz                                    done clear
  D)
             1333 Hz done clear
  View Solution play_arrow

• question_answer24)
  A source and listener are both moving towards each other with speed v/10, where v is the speed of sound. If the frequency of the note emitted by the source is f, the frequency heard by the listener would be nearly [MP PMT 1994; MP PET 2001]
  A)
             1.11 f                                        done clear
  B)
             1.22 f done clear
  C)
             f      done clear
  D)
             1.27 f done clear
  View Solution play_arrow

• question_answer25)
  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)                                                  [MP PET 1996]
  A)
             1000 Hz                                    done clear
  B)
             1066 Hz done clear
  C)
             941 Hz                                      done clear
  D)
             352 Hz done clear
  View Solution play_arrow

• question_answer26)
  A source of sound S of frequency 500 Hz situated between a stationary observer O and a wall W, moves towards the wall with a speed of 2 m/s. If the velocity of sound is 332 m/s, then the number of beats per second heard by the observer is (approximately)
  A)
             8     done clear
  B)
             6 done clear
  C)
             4     done clear
  D)
             2 done clear
  View Solution play_arrow

• question_answer27)
  A motor car blowing a horn of frequency 124vib/sec moves with a velocity 72 km/hr towards a tall wall. The frequency of the reflected sound heard by the driver will be (velocity of sound in air is 330 m/s)                      [MP PET 1997]
  A)
             109 vib/sec                             done clear
  B)
             132 vib/sec done clear
  C)
             140 vib/sec                             done clear
  D)
             248 vib/sec done clear
  View Solution play_arrow

• question_answer28)
  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                                         [MP PMT 1997]
  A)
             \[(V+S)/V\]                           done clear
  B)
             \[V/(V+S)\] done clear
  C)
             \[(V-S)/V\]                            done clear
  D)
             \[V/(V-S)\] done clear
  View Solution play_arrow

• question_answer29)
  A vehicle with a horn of frequency n is moving with a velocity of 30 m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency\[n+{{n}_{1}}\]. Then (if the sound velocity in air is 300 m/s) [CBSE PMT 1998; AIIMS 2000]
  A)
             \[{{n}_{1}}=10\,n\]             done clear
  B)
             \[{{n}_{1}}=0\] done clear
  C)
             \[{{n}_{1}}=0.1\,n\]           done clear
  D)
             \[{{n}_{1}}=-0.1\,n\] done clear
  View Solution play_arrow

• question_answer30)
  A whistle giving out 450 Hz approaches a stationary observer at a speed of 33 m/s. The frequency heard by the observer in Hz is                                                        [IIT 1997 Cancelled]
  A)
             409 done clear
  B)
             429 done clear
  C)
             517 done clear
  D)
             500 done clear
  View Solution play_arrow

• question_answer31)
  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 [EAMCET (Engg.) 1995; CPMT 1999]
  A)
             90 Hz                                        done clear
  B)
             100 Hz done clear
  C)
             91 Hz                                        done clear
  D)
             110 Hz done clear
  View Solution play_arrow

• question_answer32)
  An observer standing at station observes frequency 219 Hz when a train approaches and 184 Hz when train goes away from him. If velocity of sound in air is 340 m/s, then velocity of train and actual frequency of whistle will be [RPET 1997]
  A)
             \[15.5\,m{{s}^{-1}},\ 200\,Hz\]                                         done clear
  B)
             \[19.5\,m{{s}^{-1}},\ 205\,Hz\] done clear
  C)
             \[29.5\,m{{s}^{-1}},\ 200\,Hz\]                                         done clear
  D)
             \[32.5\,m{{s}^{-1}},\ 205\,Hz\] done clear
  View Solution play_arrow

• question_answer33)
  At what speed should a source of sound move so that stationary observer finds the apparent frequency equal to half of the original frequency                                           [RPMT 1996]
  A)
             \[\frac{v}{2}\]                       done clear
  B)
             2v done clear
  C)
             \[\frac{v}{4}\]                       done clear
  D)
             v done clear
  View Solution play_arrow

• question_answer34)
  A boy is walking away from a wall towards an observer at a speed of 1 metre/sec and blows a whistle whose frequency is 680 Hz. The number of beats heard by the observer per second is (Velocity of sound in air = 340 metres/sec  [MP PMT 1995]
  A)
             Zero                                          done clear
  B)
             2 done clear
  C)
             8     done clear
  D)
             4 done clear
  View Solution play_arrow

• question_answer35)
  The driver of a car travelling with speed 30 metres per second towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 metres per second, the frequency of the reflected sound as heard by the driver is                    [MP PMT 1996]
  A)
             720 Hz                                      done clear
  B)
             555.5 Hz done clear
  C)
             550 Hz                                      done clear
  D)
             500 Hz done clear
  View Solution play_arrow

• question_answer36)
  Two sirens situated one kilometer apart are producing sound of frequency 330 Hz. An observer starts moving from one siren to the other with a speed of 2 m/s. If the speed of sound be 330 m/s, what will be the beat frequency heard by the observer                                         [RPMT 1996; CPMT 2002]
  A)
             8     done clear
  B)
             4 done clear
  C)
             6     done clear
  D)
             1 done clear
  View Solution play_arrow

• question_answer37)
  A source of sound is travelling with a velocity 40 km/hour towards observer and emits sound of frequency 2000 Hz. If velocity of sound is 1220 km/hour, then what is the apparent frequency heard by an observer   [AFMC 1997]
  A)
             2210 Hz                                    done clear
  B)
             1920 Hz done clear
  C)
             2068 Hz                                    done clear
  D)
             2086 Hz done clear
  View Solution play_arrow

• question_answer38)
  A source of sound and listener are approaching each other with a speed of 40 m/s. The apparent frequency of note produced by the source is 400 cps. Then, its true frequency (in cps) is (velocity of sound in air = 360 m/s)         [KCET 1999]
  A)
             420 done clear
  B)
             360 done clear
  C)
             400 done clear
  D)
             320 done clear
  View Solution play_arrow

• question_answer39)
  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  [AIIMS 1999; Pb. PMT 2003]
  A)
             434.2 Hz                                  done clear
  B)
             589.3 Hz done clear
  C)
             481.2 Hz                                  done clear
  D)
             286.5 Hz done clear
  View Solution play_arrow

• question_answer40)
  A man sitting in a moving train hears the whistle of the engine. The frequency of the whistle is 600 Hz  [JIPMER 1999]
  A)
             The apparent frequency as heard by him is smaller than 600 Hz done clear
  B)
             The apparent frequency is larger than 600 Hz done clear
  C)
             The frequency as heard by him is 600 Hz done clear
  D)
             None of the above done clear
  View Solution play_arrow

• question_answer41)
  A source of sound of frequency 500 Hz is moving towards an observer with velocity 30 m/s. The speed of sound is 330 m/s. the frequency heard by the observer will be  [MP PET 2000; Kerala PMT 2005; UPSEAT 2005]
  A)
             550 Hz                                      done clear
  B)
             458.3 Hz done clear
  C)
             530 Hz                                      done clear
  D)
             545.5 Hz done clear
  View Solution play_arrow

• question_answer42)
  A source of sound of frequency 90 vibrations/ sec is approaching a stationary observer with a speed equal to 1/10 the speed of sound. What will be the frequency heard by the observer                                         [MP PMT 2000]
  A)
             80 vibrations/sec                 done clear
  B)
             90 vibrations/sec done clear
  C)
             100 vibrations/sec               done clear
  D)
             120 vibrations/sec done clear
  View Solution play_arrow

• question_answer43)
  A whistle of frequency 500 Hz tied to the end of a string of length 1.2 m revolves at 400 rev/min. A listener standing some distance away in the plane of rotation of whistle hears frequencies in the range (speed of sound = 340 m/s) [KCET 2000; AMU 1999; Pb. PET 2003]
  A)
             436 to 586                               done clear
  B)
             426 to 574 done clear
  C)
             426 to 584                               done clear
  D)
             436 to 674 done clear
  View Solution play_arrow

• question_answer44)
  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 train?s speed is reduced to 17 m/s, the frequency registered is \[{{f}_{2}}\]. If the speed of sound is 340 m/s then the ratio \[{{f}_{1}}/{{f}_{2}}\] is  [IIT-JEE (Screening) 2000]
  A)
             18/19                                        done clear
  B)
             1/2 done clear
  C)
             2     done clear
  D)
             19/18 done clear
  View Solution play_arrow

• question_answer45)
  If source and observer both are relatively at rest and if speed of sound is increased then frequency heard by observer will [RPET 2000; J & K CET 2004]
  A)
             Increases                                done clear
  B)
             Decreases done clear
  C)
             Cannot be predicted         done clear
  D)
             Will not change done clear
  View Solution play_arrow

• question_answer46)
  A source and an observer move away from each other with a velocity of 10 m/s with respect to ground. If the observer finds the frequency of sound coming from the source as 1950 Hz, then actual frequency of the source is (velocity of sound in air = 340 m/s)                        [EAMCET 1997; MH CET 2000; AFMC 2000; CBSE PMT 2001]
  A)
             1950 Hz                                    done clear
  B)
             2068 Hz done clear
  C)
             2132 Hz                                    done clear
  D)
             2486 Hz done clear
  View Solution play_arrow

• question_answer47)
  A source is moving towards an observer with a speed of 20 m/s and having frequency of 240 Hz. The observer is now moving towards the source with a speed of 20 m/s. Apparent frequency heard by observer, if velocity of sound is 340 m/s, is      [CPMT  2000; KCET 2001; MH CET 2004]
  A)
             240 Hz                                      done clear
  B)
             270 Hz done clear
  C)
             280 Hz                                      done clear
  D)
             360 Hz done clear
  View Solution play_arrow

• question_answer48)
  A siren placed at a railway platform is emitting sound of frequency 5 kHz. A passenger sitting in a moving train A records a frequency of 5.5 kHz while the train approaches the siren. During his return journey in a different train B he records a frequency of 6.0 kHz while approaching the same siren. The ratio of the velocity of train B to that of train A is [IIT-JEE (Screening) 2002]
  A)
             242/252                                   done clear
  B)
             2 done clear
  C)
             5/6 done clear
  D)
             11/6 done clear
  View Solution play_arrow

• question_answer49)
  A whistle revolves in a circle with an angular speed of 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 heard by an observer, which is far away from the centre in the same plane? (v = 340 m/s) [CBSE PMT 2002]
  A)
             333 Hz                                      done clear
  B)
             374 Hz done clear
  C)
             385 Hz                                      done clear
  D)
             394 Hz done clear
  View Solution play_arrow

• question_answer50)
  A Siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s, frequency of the sound to be heard by the listener is (take velocity of sound as 330 m/s) [CPMT 1996; AIIMS 2002; Pb. PMT 2001]
  A)
             733.3 Hz                                  done clear
  B)
             644.8 Hz done clear
  C)
             481.2 Hz                                  done clear
  D)
             286.5 Hz done clear
  View Solution play_arrow

• question_answer51)
  A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before and after passing of the car is 11 : 9. If the speed of sound is v, the speed of the car is  [MP PET 2002]
  A)
             \[\frac{1}{10}v\]                  done clear
  B)
             \[\frac{1}{2}v\] done clear
  C)
             \[\frac{1}{5}v\]                    done clear
  D)
             v done clear
  View Solution play_arrow

• question_answer52)
  What should be the velocity of a sound source moving towards a stationary observer so that apparent frequency is double the actual frequency (Velocity of sound is v) [MP PMT 2002]
  A)
             v     done clear
  B)
             2v done clear
  C)
             \[\frac{v}{2}\]                       done clear
  D)
             \[\frac{v}{4}\] done clear
  View Solution play_arrow

• question_answer53)
  Two trains are moving towards each other at speeds of 20 m/s and 15 m/s relative to the ground. The first train sounds a whistle of frequency 600 Hz. the frequency of the whistle heard by a passenger in the second train before the train meets is (the speed of sound in air is 340 m/s) [UPSEAT 2002]
  A)
             600 Hz                                      done clear
  B)
             585 Hz done clear
  C)
             645 Hz                                      done clear
  D)
             666 Hz done clear
  View Solution play_arrow

• question_answer54)
  A small source of sound moves on a circle as shown in the figure and an observer is standing on \[O\]. Let \[{{n}_{1}},\ {{n}_{2}}\] and \[{{n}_{3}}\]be the frequencies heard when the source is at \[A,\ B\] and \[C\] respectively. Then                    [UPSEAT 2002]
  A)
             \[{{n}_{1}}>{{n}_{2}}>{{n}_{3}}\] done clear
  B)
             \[{{n}_{2}}>{{n}_{3}}>{{n}_{1}}\] done clear
  C)
             \[{{n}_{1}}={{n}_{2}}>{{n}_{3}}\] done clear
  D)
             \[{{n}_{2}}>{{n}_{1}}>{{n}_{3}}\] done clear
  View Solution play_arrow

• question_answer55)
  A source and an observer approach each other with same velocity 50 m/s. If the apparent frequency is 435 sec?1, then the real frequency is                                                    [CPMT 2003]
  A)
             320 s?1                                      done clear
  B)
             360 sec?1 done clear
  C)
             390 sec?1                                 done clear
  D)
             420 sec?1 done clear
  View Solution play_arrow

• question_answer56)
  A source emits a sound of frequency of 400 Hz, but the listener hears it to be 390 Hz. Then [Orissa JEE 2003]
  A)
             The listener is moving towards the source done clear
  B)
             The source is moving towards the listener done clear
  C)
             The listener is moving away from the source done clear
  D)
             The listener has a defective ear done clear
  View Solution play_arrow

• question_answer57)
  Doppler effect is applicable for                               [AFMC 2003]
  A)
             Moving bodies                     done clear
  B)
             One is moving and other are stationary done clear
  C)
             For relative motion done clear
  D)
             None of these done clear
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• question_answer58)
  A source and an observer are moving towards each other with a speed equal to \[\frac{v}{2}\] where \[v\] is the speed of sound. The source is emitting sound of frequency n. The frequency heard by the observer will be                      [MP PET 2003]
  A)
             Zero                                          done clear
  B)
             \[n\] done clear
  C)
             \[\frac{n}{3}\]                      done clear
  D)
             \[3n\] done clear
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• question_answer59)
  When an engine passes near to a stationary observer then its apparent frequencies occurs in the ratio 5/3.  If the velocity of engine is                                                 [MP PMT 2003]
  A)
             540 m/s                                   done clear
  B)
             270 m/s done clear
  C)
             85 m/s                                     done clear
  D)
             52.5 m/s done clear
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• question_answer60)
  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 :                                      [UPSEAT 2004]
  A)
             248 Hz                                      done clear
  B)
             244 Hz done clear
  C)
             240 Hz                                      done clear
  D)
             230 Hz done clear
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• question_answer61)
  A person carrying a whistle emitting continuously a note of 272 Hz is running towards a reflecting surface with a speed of 18 km/hour. The speed of sound in air is \[345m{{s}^{-1}}\]. The number of beats heard by him is  [Kerala (Engg.) 2002]
  A)
             4     done clear
  B)
             6 done clear
  C)
             8     done clear
  D)
             3 done clear
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• question_answer62)
  A bus is moving with a velocity of 5 m/s towards a huge wall. the driver sounds a horn of frequency 165 Hz. If the speed of sound in air is 355 m/s, the number of beats heard per second by a passenger on the bus will be [KCET 2001; BHU 2002]
  A)
             6     done clear
  B)
             5 done clear
  C)
             3     done clear
  D)
             4 done clear
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• question_answer63)
  A source of sound of frequency 256 Hz is moving rapidly towards a wall with a velocity of 5m/s. The speed of sound is 330 m/s. If the observer is between the wall and the source, then beats per second heard will be            [UPSEAT 2002]
  A)
             7.8 Hz                                       done clear
  B)
             7.7 Hz done clear
  C)
             3.9 Hz                                       done clear
  D)
             Zero done clear
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• question_answer64)
  The apparent frequency of a note, when a listener moves towards a stationary source, with velocity of 40 m/s is 200 Hz. When he moves away from the same source with the same speed, the apparent frequency of the same note is 160 Hz. The velocity of sound in air is (in m/s)     [KCET 1998]
  A)
             360 done clear
  B)
             330 done clear
  C)
             320 done clear
  D)
             340 done clear
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• question_answer65)
  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)
             5%  done clear
  B)
             20% done clear
  C)
             Zero                                          done clear
  D)
             0.5% done clear
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