Page 3 - WORKSHEET -2 CH 15 CLASS XI

12. A SONAR system fixed in a submarine operates at a frequency 40.0 kHz. An enemy
-1
submarine moves towards the SONAR with a speed of 360 km h . What is the frequency of
-1
sound reflected by the submarine? Take the speed of sound in water to be 1450 ms .

13. A train, standing in a station-yard, blows a whistle of frequency 400 Hz in still air. The wind
-1
starts blowing in the direction from the yard to the station with a speed of 10 ms . What are
the frequency, wavelength, and speed of sound for an observer standing on the station’s
platform? Is the situation exactly identical to the case when the air is still and the observer runs
-1
-1
towards the yard at a speed of 10 ms ? The speed of sound in still air can be taken as 340 ms ?