A submarine sends a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?
The time taken by the sonar pulse to go from the submarine to cliff will be half of this time:
= 
= 0.51 second
We know that,
Speed =
1531 = 
Distance = 1531 × 0.51
= 780.8 m
2