A fish finder uses a sonar device that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 85 m, what is the minimum time between pulses (in fresh water)?

0.3106 seconds

Explanation:

Frequency= 20,000-Hz

The speed of echoes sounds can be calculated using the expression below;

Y= ( 2x/t) eqn(1)

t= overall time taken

x = maximum depth = 230m

Y= speed of echoes sounds

Speed of sound in water= 1,481 m/s which is a constant with little variation.

If we substitute the given values into eqn(1) we have

1481 = (2× 230)/ t

1481 × t= 460

t=460/1481

t=0.3106 seconds

Hence, the minimum time between pulses (in fresh water) is 0.3106 seconds