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## 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

f

_{ship}= (v+v

_{ship}/v+v

_{whale})f

_{whale}

## The Attempt at a Solution

To find the frequency of the reflected waves, I used the above equation with v

_{ship}=0 and v

_{whale}=-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.