Question

A dolphin in ${25}^{\circ }$C sea water emits a sound directed toward the bottom of the ocean 150 m below. How much time passes before it hears an echo?
(Take speed of sound in sea water at ${25}^{\circ }$ C = 1530 m/s)

Answer 1

To hear an echo , sound will come back to dolphin after reflection from the bottom of sea ,

total distance travelled by sound , $d=150+150=300m$ ,

given speed of sound in sea water , $v=1530m/s$ ,

therefore , time after which dolphin hears an echo ,

$t=d/v=300/1530=0.196=0.20s$