# Spund sources

## Homework Statement

A sound source moves at a constant velocity. A listener is standing at a distance L away from it. Given that the source moves in a straight line at a right angle to the listener and starts closest to the listener (ie at t=0) deduce an expression for the frequency heard by the listener in relation to time.

## Homework Equations

fl=fs(v/(v-vs))
where l is listener and s is source

## The Attempt at a Solution

It's obviously Doppler effect related.
So far I’ve done T=1/fs
And gotten
fl=v/T(v-vs)

But unsure how to get L into the equation.
Surely VT is the distance travelled by the wave and vsT is λs. Is there any orientation where L can be introduced? Or is this version correct?

take in the velocity component of the source away from the observer at each instant of time in the governing equation.

(edit) So you mean f=v/T(vs-v)??

Last edited:
No
O(t=0)----------------------->vt(point A)(source)
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Point B(you)
I want you to find the component of source’s(A) velocity
Along the line joining point A & point B at an instant t
And plug that velocity into your equation for vs.