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## Homework Statement

Assuming the speed of sound is 338 m/s:

A bat moving at 6.2 m/s is chasing a flying insect. The bat emits a 53 KHz chirp and receives an echo at 53.6 KHz. At what speed is the bat catching up on its prey?

## Homework Equations

[tex]f^{'}[/tex]=[ ([tex]V_{Air}[/tex] + [tex]V_{observer}[/tex]) [tex]/[/tex] ([tex]V_{Air}[/tex] - [tex]V_{source}[/tex] ] * f

## The Attempt at a Solution

I assumed that since the objects are moving in the same direction I said that the signs are different, but I don't know which one should be positive or negative because normally the signs are the same because Doppler effect usually comes into play when the objects are moving towards or away from each other, but these are moving in the same direction, while the bat is moving quicker and accelerating towards the prey....I just plugged in the numbers, but I don't know which way to work with it....Help?

My answers for Vo (+) and Vs (-) was...Vo = 2.4 m/s

With the Vo (-) and Vs (+) I arrived at...Vo = 10.096