
Ultrasound and SONAR

Let us take a look at a typical question about SONAR and depth at sea:
A ship sends a pulse of ultrasound and receives an echo 0·3 seconds later. If the speed of sound in water is 1500 m/s calculate its depth.

speed = distance / time
... distance = speed × time
distance = 1500 × 0·3 = 450 m
BUT this is the total distance travelled by the sound  so the depth is half of this.
Depth = 450 / 2 = 225 m 
Be careful  when dealing with reflected sound (echoes) exam questions often try to trick you into using the total distance, not the one you want.
