# Homework Help: Doppler Effect II (Both observer and source in motion)

1. Jul 11, 2007

### exi

1. The problem statement, all variables and given/known data

You're flying in an aircraft at 46 m/s. An eagle flies directly towards you at 11 m/s. Speeds are relative to ground.

The eagle emits a cry at 3400 Hz, and the speed of sound is 330 m/s. What frequency do you hear?

2. Relevant equations

$$f_o = f_s\left( \frac{1\pm\frac{v_o}{v}}{1\mp\frac{v_s}{v}} \right)$$

Because the observer and source are both moving towards each other (presumably?),

$$f_o = f_s\left( \frac{1+\frac{v_o}{v}}{1-\frac{v_s}{v}} \right)$$

3. The attempt at a solution

Seems simple enough, but

$$f_o = 3400\left( \frac{1+\frac{46}{330}}{1-\frac{11}{330}} \right)$$

Works out to 4902.8213 Hz, a wrong answer. This problem seemed straightforward, but I'm not sure what I'm missing.

Last edited: Jul 11, 2007
2. Jul 11, 2007

### Dick

Check your math. That's not what I get.

3. Jul 11, 2007

### exi

Don't I feel silly, part 2.

4007.5235 Hz. I've got only one remaining shot at that problem; I didn't make any other conceptual mistakes, correct?

4. Jul 11, 2007

### Dick

That's what I get, but I'm not claiming infallibility.

5. Jul 11, 2007

### exi

It's correct.

Thanks much, sir; I'll just whistle and blame my calculator now.