The Total solution for NCERT class 6-12
A SONAR (sound navigation and ranging) uses ultrasonic waves todetect and locate objects under water. In a submarine equipped with a SONAR thetime delay between generation of a probe wave and the reception of its echoafter reflection from an enemy submarine is found to be 77.0 s. What is thedistance of the enemy submarine? (Speed of sound in water = 1450 m s–1).
Let the distance between the ship and the enemy submarine be ‘S’.
Speed of sound in water = 1450 m/s
Time lag between transmission and reception of Sonar waves = 77 s
In this time lag, sound waves travel a distance which is twice thedistance between the ship and the submarine (2S).
Timetaken for the sound to reach the submarine
∴ Distance between the ship andthe submarine (S)= 1450 × 38.5 = 55825 m = 55.8 km