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**Doppler shift with microwaves....i think....**

## Homework Statement

Microwaves, which travel at the speed of light, are reflected from a distant airplane approaching the microwave source. It is found that when the reflected waves are beat against the waves radiating from the source, the beat frequency is given by 969 Hz. If the source microwaves are 150 mm in wavelength, what is the approach speed (in km/h) of the airplane?

## Homework Equations

I think that the 3 relevant equations are [tex]C=\lambda[/tex] [tex]\nu[/tex]

and dopplers equation

[tex]F= \left(v+v_{r}\right)/\left(v+v_{s}\right)*F_{0}[/tex]

[tex]F_{beat} = \left|F_1-F_2\right|[/tex]

## The Attempt at a Solution

My attempt at the solution is to take the speed of light, divide by .150 m, to get the frequency of my microwave. This value gives me [tex]\nu =1.998*10^9[/tex].

I then put it into the beat formula and solve for [tex]F_1= 1.997*10^9[/tex].

I would then sub into my dopplers formula, except i don't know if the source is moving towards it or if it is moving away. I am also not sure if i did any of this right because the microwave frequency is so high, that the beats have virtually no affect. Any insight would be appreciated, thank you in advance.

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