- #1

dingo_d

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## Homework Statement

The observer sees first spaceship that is moving from the right towards him with the speed [itex]v_r=0.6c[/itex], and the second ship that is coming from the left with the speed [itex]v_l=0.8c[/itex].

If the first ship emits a signal with the frequency of [itex]10^4[/itex] Hz (measured in the reference frame of the ship - where the ship is standing still), what is the frequency of the signal that the observer measures?

## Homework Equations

Lorentz transformations.

## The Attempt at a Solution

I am wondering if I am thinking right on this one. Since everything is relative, I can look at this as if the ship is standing still, and the observer is moving towards him with the speed of 0.6 c. And then, since it's moving towards the signal it will see it being blue shifted - coming towards him, right?

So using the formula:

[itex]\nu'=\nu\sqrt{\frac{1+\beta}{1-\beta}}[/itex]

I get that the frequency measured by observer is [itex]\nu'=2\times 10^4[/itex] Hz.

(higher frequency means blue shifted, right?).

Is this correct, or did I messed sth up?

Thanks :)