NEET Physics Musical Sound and Dopplers Effect Online Test Set A

1. A man is watching two trains, one leaving and the other coming in with equal speeds of 4m/sec. If they sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air = 320 m/sec) will be equal to

2. A train approaching a hill at a speed of 60 km/hour sounds a whistle of frequency 600 Hz when it is at a distance of 1 km from the hill. Wind is blowing in the direction of the train with a speed of 60 km/h. Find the frequency of the whistle heard by an observer on the hill: (Velocity of sound in air = 1200 km/h)

3. A source producing sound of frequency 170 Hz is approaching a stationary observer with a velocity 17 ms^–1. The apparent change in the wavelength of sound heard by the observer is (speed of sound in air = 340 ms^–1)

4. Two trains move towards each other with the same speed. The speed of sound is 340 m/s. If the height of the tone of the whistle of one of them heard on the other changes 9/8 times, then the speed of each train should be

5. Two trains are moving towards each other with speeds of 20m/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)

6. A police car moving at 22 m/s, chases a motorcyclist. The policeman sounds his horn at 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. The speed of the motorcycle, if it is given that he does not observe any beats is

7. A sound source emits frequency of 180 Hz when moving towards a rigid wall with speed 5 m/s and an observer is moving away from wall with speed 5 m/s. Both source and observer moves on a straight line which is perpendicular to the wall. The number of beats per second heard by the observer will be [Speed of sound = 355 m/s]

8. The power of a sound from the speaker of a radio is 20 milliwatt. By turning the knob of the volume control the power of sound is increased to 400 milliwatt. The power increases (indecibel) as compared to the original power is:

9. A whistle producing sound waves of frequencies 9500 HZ and above is approaching a stationary person with speed vms^–1. The velocity of sound in air is 300 ms^–1. If the person can hear frequencies upto a maximum of 10,000 HZ, the maximum value of v upto which he can hear whistle is

10. A band playing music at frequency f is moving towards a wall at a speed v_b. A motorist is following the band with a speed v_m. If v is the speed of sound, the expression for the beat frequency heard by the motorist is

11. A whistle of frequency 385 Hz rotates in a horizontal circle of radius 50 cm at an angular speed of 20 radians s^–1. The lowest frequency heard by a listener a long distance away at rest with respect to the centre of the circle, given velocity of sound equal to 340 ms^–1, is

12. A is singing a note and at the same time B is singing a note with exactly one-eight the frequency of the note of A. The energies of the two sounds are equal. The amplitude of the note of B is:

13. The musical interval between two tones of frequencies 320 Hz and 240 Hz is:

14. Assertion : Doppler formula for sound wave is symmetric with respect to the speed of source and speed of observer.
Reason : Motion of source with respect to stationary observer is not equivalent to the motion of an observer with respect to stationary source.

15.

16.

17. If wind blows from a stationary sounding object to a stationary listener, then the apparent frequency n' and actual frequency n are related as

18. Choose the false statement(s) from the following.
I. Change in frequency due to Doppler effect will be positive if the distance between source and listenerincreases.
II. Change in frequency due to Doppler effect will be negative if the distance between source and listener

19. A train moving at a speed v_s towards a stationary observer on a platform emits sound of frequency f and velocity v. Then the apparent frequency heard by him is

20. For which of the following cases, there will be no Doppler effect?

21. Doppler shift in frequency does not depend upon

22. Doppler phenomena is related with

23. Doppler's effect in sound takes place when source and observer are

24. A source of sound is moving with a uniform speed along a circle. The frequency of sound as heard by listener stationed at the centre of the path

25. The loudness and pitch of a sound depends on