# Plz Solve this - Relating to Doppler frequency

1. Nov 17, 2009

### jerin_007

1. The problem statement, all variables and given/known data
For a mobile receiver operating at a frequency of 900MHz and moving at 100Km/hr.

2. Relevant equations
Find Doppler frequency.

3. The attempt at a solution

2. Nov 17, 2009

### tiny-tim

Welcome to PF!

Hi jerin_007! Welcome to PF!

Show us what you've tried, and where you're stuck, and then we'll know how to help!

3. Nov 17, 2009

### jerin_007

Its just a single formula.. I need to know that.

4. Nov 18, 2009

### tiny-tim

ok …

then what equations has your professor given you on the subject (or what equations does your book give you)?

and which of those equations do you think will work in this case?

5. Nov 18, 2009

### jerin_007

If that so.. i could have found it.. All i know is how to find doppler spread.. But doppler frequency i cant think of and it isn't there in the book.

6. Nov 18, 2009

### Staff: Mentor

You obviously have access to a computer with an internet connection. Search for Doppler shift or Doppler effect, and see what you find.

7. Nov 18, 2009

### phycud

This looks like a simple doppler shift problem:

you should state which direction of motion the moblie phone is in, this determines whether the the phone is redshifting or blueshifting, so that we know what formulas to use.

i'm going to guess you're dropping the mobile phone down something, which means redshifting.

Which should be (correct me if i'm wrong): f1 = f(C1/(C1+Vs))

Where C1 = Speed of sound (343 ms-1)
f = is the original frequency (900hz)
Vs = the speed of the source (mobile phone 100km/hr)
f1 = new frequency

The phone is redshifting therefore the frequency will be less, i'll let you work the rest out.

quite interesting too, i have an exam question similar to this that is very soon.

8. Nov 19, 2009

### jerin_007

Thanks phycud....