Question

A dolphin emits ultrasound at 100kHz and uses the timing of reflections to determine the position of objects in the water. What is the wavelength of this ultrasound? Assume that temperature of water is 20C.

Answer 1

To answer the question above, 
First, let's determine the speed of sound under the water.
S
peed of sound in water at 20oC = 1482m/s 

So λ = v/f = 1482m/s/(100kHz) I'm assuming your frequency is 100kHz 

So λ would be = 0.0148m
I hope my answer helped you.