Doppler's Effect PYQs: JEE Mains Physics

Showing 1–32 of 32 questions

1. 1. A car \(P\) travelling at \(20\,ms ^{-1}\) sounds its horn at a frequency of \(400\,Hz\). Another car \(Q\) is travelling behind the first car in the same direction with a velocity \(40\,ms ^{-1}\). The frequency heard by the passenger of the car \(Q\) is approximately \(.......\,Hz\) [Take, velocity of sound \(=360\,ms ^{-1}\) ] 2023 Easy
2. 2. A person driving car at a constant speed of \(15\,m / s\) is approaching a vertical wall. The person notices a change of \(40\,Hz\) in the frequency of his car's horn upon reflection from the wall. The frequency of horn is ............ \(Hz\). (Given : Speed of sound : \(330\,m / s\) ) 2023 Hard
3. 3. A person observes two moving trains, '\(A\)' reaching the station and '\(B\)' leaving the station with equal speed of \(30\,m / s\). If both trains emit sounds with frequency \(300\,Hz\), (Speed of sound : \(330\,m / s\) ) approximate difference of frequencies heard by the person will be \(..........Hz\) 2023 Medium
4. 4. A train blowing a whistle of frequency \(320\,Hz\) approaches an observer standing on the platform at a speed of \(66\,m / s\). The frequency observed by the observer will be (given speed of sound \(=330\,ms ^{-1}\) ) \(.............Hz\). 2023 Easy
5. 5. The engine of a train moving with speed \(10\,ms ^{-1}\) towards a platform sounds a whistle at frequency \(400\,Hz\). The frequency heard by a passenger inside the train is \(........\,Hz\) (neglect air speed. Speed of sound in air \(330\,ms ^{-1}\) ) 2023 Medium
6. 6. An observer is riding on a bicycle and moving towards a hill at \(18\,km\,h ^{-1}\). He hears a sound from a source at some distance behind him directly as well as after its reflection from the hill. If the original frequency of the sound as emitted by source is \(640\,\,Hz\) and velocity of the sound in air is \(320\,m / s\), the beat frequency between the two sounds heard by observer will be \(...Hz\). 2022 Easy
7. 7. An observer moves towards a stationary source of sound with a velocity equal to one-fifth of the velocity of sound. The percentage change in the frequency will be \(\dots \;\)% 2022 Medium
8. 8. The frequency of echo will be \(.......Hz\) if the train blowing a whistle of frequency \(320\,Hz\) is moving with a velocity of \(36\,km / h\) towards a hill from which an echo is heard by the train driver. Velocity of sound in air is \(330\,m / s\). 2022 Hard
9. 9. When a car is approaching the observer, the frequency of horn is \(100 Hz\). After passing the observer, it is \(50\,Hz\). If the observer moves with the car, the frequency will be \(\frac{ x }{3} Hz\) where \(x =.....\) 2022 Hard
10. 10. A source and a detector move away from each other in absence of wind with a speed of \(20\, {m} / {s}\) with respect to the ground. If the detector detects a frequency of \(1800\, {Hz}\) of the sound coming from the source, then the original frequency of source considering speed of sound in air \(340\, {m} / {s}\) will be \({Hz}\) 2021 Easy
11. 11. The frequency of a car horn encountered a change from \(400\, {Hz}\) to \(500\, {Hz}\), when the car approaches a vertical wall. If the speed of sound is \(330\, {m} / {s}\). Then the speed of car is \(.....\,{km} / {h} .\) 2021 Easy
12. 12. Two cars are approaching each other at an equal speed of \(7.2\, km / hr\). When they see each other, both blow horns having frequency of \(676\, Hz\). The beat frequency heard by each driver will be \(.....\, Hz\). [Velocity of sound in air is \(340\,m / s .]\) 2021 Easy
13. 13. Two cars \({X}\) and \({Y}\) are approaching each other with velocities \(36\; {km} / {h}\) and \(72\; {km} / {h}\) respectively. The frequency of a whistle sound as emitted by a passenger in car \({X}\), heard by the passenger in car \({Y}\) is \(1320 \;{Hz}\). If the velocity of sound in air is \(340\; {m} / {s}\), the actual frequency of the whistle sound produced is ........ \(Hz.\) 2021 Easy
14. 14. A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from \(440\, Hz\) to \(480 \,Hz ,\) when it gets reflected from the wall. If the speed of sound in air is \(345 \,m / s ,\) then the speed of the car is \(.......km/hr\) 2020 Medium
15. 15. A stationary observer receives sound from two identical tuning forks, one of which approaches and the other one recedes with the same speed (much less than the speed of sound). The observer hears \(2\; beats/sec\). The oscillation frequency of each tuning fork is \(v_{0}=1400 \;\mathrm{Hz}\) and the velocity of sound in air is \(350\; \mathrm{m} / \mathrm{s}\). The speed of each tuning fork is close to  2020 Hard
16. 16. The driver of a bus approaching a big wall notices that the frequency of his bus's horn changes from \(420\, Hz\) to \(490\, Hz ,\) when he hears it after it gets reflected from the wall. Find the speed of the bus (in \(kmh^{-1}\)) if speed of the sound is \(330\, ms ^{-1}\). 2020 Hard
17. 17. 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 a speed of \(10 \,km/h.\) If the wave speed is \(330\,m/s,\) the frequency heard by the running person shall be close to...... \(Hz\) 2019 Easy
18. 18. A person standing on an open ground hears the sound of a jet aeroplane, coming from north at an angle \(60^o\) with ground level. But he finds the aeroplane right vertically above his position. If \(\upsilon \) is the speed of sound, speed of the plane is 2019 Easy
19. 19. A source of sound \(S\) is moving with the velocity of \(50\,m/s\) towards a stationary observer. The observer measures the frequency of the sound as \(1000\,Hz.\) What will be the apparent frequency of the source when it is moving away from the observer after crossing him ... \(Hz\) ? (Take velocity of sound in air is \(350\,m/s\) ) 2019 Easy
20. 20. 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 \(= 300\, m/s\)) 2019 Medium
21. 21. A submarine \((A)\) travelling at \(18\, km/hr\) is being chased along the line of its velocity by another submarine \((B)\) travelling at \(27\, km/hr\). \(B\) sends a sonar signal of \(500\, Hz\) to detect \(A\) and receives a reflected sound of frequency \(v\). The value of \(v\) is close to ... \(Hz\) (Speed of sound in water \(= 1500\, ms^{-1}\)) 2019 Hard
22. 22. 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 2019 Hard
23. 23. Two cars \(A\) and \(B\) are moving away from each other in opposite directions. Both the cars are moving with a speed of \(20\, ms^{-1}\) with respect to the ground. If an observer in car \(A\) detects a frequency \(2000\, Hz\) of the sound coming from car \(B\), what is the natural frequency of the sound source of car \(B\) ....  \(Hz\) ? (speed of sound in air \(= 340\, ms^{-1}\)) 2019 Hard
24. 24. 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 ... \(m/s\) 2019 Medium
25. 25. 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 \(5\, beats\) per second. If the velocity of sound in air is \(340\, m/s\), the frequency of the horn of the toy car is close to  ... \(Hz\) 2016 Medium
26. 26. Two engines pass each other moving in opposite directions with uniform speed of \(30\,m/s\) . One of them is blowing a whistle of frequency \(540\,Hz.\) Calculate the frequency heard by driver of second engine before they pass each other  ... \(Hz\). Speed of sound is \(330\,m/sec\) 2016 Easy
27. 27. A bat moving at \(10\,ms^{-1}\) 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 close to (speed of sound \(= 320\,ms^{-1}\) ) 2015 Hard
28. 28. A source of sound emits sound waves at frequency \(f_0\). It is moving towards an observer with fixed speed \(v_s\) (\(v_s < v\), where \(v\) is the speed of sound in air). If the observer were to move towards the source with speed \(v_0\), one of the following two graphs (\(A\) and \(B\)) will given the correct variation of the frequency \(f\) heard by the observer as \(v_0\) is changed The variation of \(f\) with \(v_0\) is given correctly by
    2015 Easy
29. 29. A train is moving on a straight track with speed \(20\ ms^{-1}\). 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 \(=320\) \(ms^{-1}\) ) close to .... \(\%\) 2015 Hard
30. 30. 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 ..... \(Hz\) (Speed of sound \(= 343\,m/s\) ) 2014 Easy
31. 31. \(A\) 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 ..... \(Hz\)
    2013 Medium
32. 32. An engine approaches a hill with a constant speed. When it is at 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 .... \(m/s\) 2013 Easy

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