**Question** 1:

A submarine emits 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?

**Answer**:

Time taken by the sonar pulse to return, *t *= 1.02 s

Speed of sound in salt water, *v *= 1531 m s^{−1}

Total distance covered by the sonar pulse = Speed of sound × Time taken

Total distance covered by the sonar pulse …..(i)

Let *d* be the distance of the cliff from the submarine.

Total distance covered by the sonar pulse = 2*d*

⇒2d=1561.62 [From (i)]⇒d=780.81 m