# Frequency of relected wave

1. Aug 3, 2014

### somecelxis

1. The problem statement, all variables and given/known data
A stationary boat emits a sonar wave of frequency f to a school of fish which is moving a velocity u towards the boat. The sonar wave is then reflected by the school of fish. If v is the velocity of the sonar wave in water, the frequency of the wave reflected by the fish is

2. Relevant equations

3. The attempt at a solution
My ans is same as the working (first part) . I cant understand with the 2nd part . in my opinion, the frequency reflected by the fish is same as the frequency received by the fish . my ans is (( v+u)/ v ) x f . why ? is my concept wrong?

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2. Aug 4, 2014

### SammyS

Staff Emeritus
Is it asking for the frequency of the reflected wave as sensed by the fish (or equivalently, by an observer moving with the same velocity as the fish)? Or is it asking for the frequency of the reflected wave as sensed by a stationary observer?

3. Aug 8, 2014

### somecelxis

hi , the question ask for the frequncy reflected by the school of fish am i right? now the fish act as the sound source... and the frequncy of the sound reflected by the fish = freuqency received by the fish . so i have (( v+u)/ v ) x f ... this is the whole question.

the sample ans is giving the frequncy of the sound heard by the observer on the boat after the reflection by the fish(source) ?am i right?