Doppler Effect in Light Waves

Q. An engine running at speed v/10 sounds a whistle of frequency 600 Hz. A passenger in a train coming from the opposite side at speed v/15 experiences this whistle to be of frequency f. If v is speed of sound in air and there is no wind, f is nearest to

1. 711 Hz
2. 630 Hz
3. 580 Hz
4. 510 Hz
   

Q. A wall is moving with velocity u and a source of sound moves with velocity u/2 in the same direction as shown in the figure. Assuming that the sound travels with velocity 10u, the ratio of incident sound wavelength on the wall to the reflected sound wavelength by the wall is equal to

1. 9:11
2. 11:9
3. 4:5
4. 5:4

Q. A boy is walking away from a wall at a speed of 1m/s in a direction at right angle to the wall. As he walks, he blows a whistle steadily. An observer towards whom the boy is walking hears 4 beats per second. If the speed of sound is 340m/s, what is the frequency of the whistle?

1. 680 Hz
2. 720 Hz
3. 760 Hz
4. 800 Hz

Q. An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency $10\text{GHz}$. What is the frequency in GHz of the microwave measured by the observer?
(speed of light $=3\times {10}^8{\text{ms}}^{-1}$). Answer the nearest integer.