It has to do with echoes

Question

As a ship approaches a cliff, it's siren is sounded and the echo is heated in the ship after 12 seconds. 2.1 minutes later the siren is sounded again and the echo is heated 8 seconds later . If the speed of sound in air is 340ms-1, calculate the velocity at which the ship is approaching the cliff

Answer 1

We need to find the distance traveled for 2.1 min.

To hear the echo, the sound traveled to the cliff and back, twice the distance from the boat to cliff.

The distance from boat to cliff should be half of it.

Beginning distance = 340 x 12/2 = 2040 m.

End distance = 340 x 8/2 = 1360 m.

Distance traveled = 2040 - 1360 = 680 m.

Speed = distance traveled/time

          = 680/(2.1*60)

          = 3.01 m/sec.

The boat approaching the cliff at 3.01m/sec or about 3m/sec.

Note, the velocity is a speed with direction.