# Homework Help: Heart beat doppler effect

1. Nov 5, 2007

### azila

1. The problem statement, all variables and given/known data
A 1.50-MHz sound wave travels through a pregnant woman’s abdomen and is reflected from the fetal heart wall of her unborn baby. The heart wall is moving toward the sound receiver as the heart beats. The reflected sound is then mixed with the transmitted sound, and 85 beats per second are detected. The speed of sound in body tissue is 1520m/s .
Calculate the speed of the fetal heart wall at the instant this measurement is made.
in m/s.

2. Relevant equations
fh= fs((v+vh)/(v))

3. The attempt at a solution

Ok, so first I converted my frequency of sound from 1.50 mHz to hertz. Then I plugged in everything. I used v as 1520 m/s. and Vh as 85 beats per second. However, I was wondering shouldn't the beats per second be converted?? This is the equationt that the teacher gave in class. I guess I am not plugging in the right numbers... Any help would be appreciated. Thanks.

2. Nov 5, 2007

### Dick

What would you convert 85 beats per second to? The beats per second represents the difference between the emitted sound frequency and the detected sound frequency.

3. Nov 6, 2007

### azila

would i use the equation,
change in frequency = frequency toward - frequency away..

4. Nov 6, 2007

Yesssss.