Frequency of Reflected Underwater Sound Wave

  • Thread starter betamu
  • Start date
  • #1
12
3

Homework Statement


The sound source of a ship’s sonar system operates at
a frequency of 18.0 kHz. The speed of sound in water (assumed
to be at a uniform 20°C) is 1482 m/s. What is the difference
in frequency between the directly radiated waves and the waves
reflected from a whale traveling directly toward the ship at
4.95 m/s ? The ship is at rest in the water.

Homework Equations


fship = (v+vship/v+vwhale)fwhale

The Attempt at a Solution


To find the frequency of the reflected waves, I used the above equation with vship=0 and vwhale=-4.95m/s. Found the reflected frequency to be 18060.32Hz, which means a 60Hz difference. My textbook says it should be double that, 120Hz.
 

Answers and Replies

  • #2
950
418
What you have determined is the frequency shift experienced by the whale if the whale were the receiver. Bouncing off the whale and returning to the ship doubles the effect. It’s as if the whale is now an emitter at the Doppler shifted frequency and the ship hears that frequency Doppler shifted again

By the way, I think in trying to do it in one step you’ve put f0 on the wrong side of the equation
 
  • Like
Likes CWatters
  • #3
594
197
Step 1: Whale is listener and listener is moving
Step 2: Whale is source and source is moving.
 

Related Threads on Frequency of Reflected Underwater Sound Wave

  • Last Post
Replies
12
Views
312
Replies
7
Views
4K
  • Last Post
Replies
1
Views
9K
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
1
Views
888
  • Last Post
Replies
4
Views
4K
  • Last Post
Replies
1
Views
7K
  • Last Post
Replies
8
Views
2K
Top