Relativistic Doppler Effect and a Baseball

[SOLVED] Relativistic Doppler Effect and a Baseball

Homework Statement

A baseball coach uses a radar device to measure the speed of an approaching pitched baseball. This device sends out electromagnetic waves with frequency $$f_0$$ and then measures the shift in frequency $$\Delta f$$ of the waves reflected from the moving baseball.

If the fractional frequency shift produced by a baseball is $$\frac{\Delta f}{f_0}$$ 2.88×10−7, what is the baseball's speed? (Hint: Are the waves Doppler-shifted a second time when reflected off the ball?)

Homework Equations

$$u = \frac{c((\frac{\delta f}{f_0})^2) - 1}{\frac{\delta f}{f_0})^2 + 1}$$

The Attempt at a Solution

I tried putting the variables in, but becasue there is a double doppler shift, the asnwer was incorrect. Was is the best way to do this question when a Double Shift occurs?

Any ideas gratly appreciated,

TFM

Edit: in the formulas, that should be a big Delta not a small Delta, Sorry

Related Introductory Physics Homework Help News on Phys.org
If the DELf given is actually twice the doppler shift we're interested in... then what DELf should we use?

Would it be half?

TFM

exactly

When I enter it into the equation, it just seems to spit out the speed of Light...?

TFM

You're equation might not be quite right...

namely: where you have Delf / f; i think it should be (observed f) / (source f).
Del f / f = (source f - observed f) / (source f)

.. try it the other?

I was using the wrong formula

The equation to use is:

$$\frac{\Delta f}{f_0} = \frac{u}{c}$$

Thanks for the assistance, lzkelley,

TFM