Question

A blood-flow meter emits a 1.1-MHz ultrasound pulse to measure the speed of blood moving directly away from the meter. The meter’s sensor detects the pulse reflected back from the blood at a frequency 21 Hz lower than the emitted frequency. Take the speed of sound in the tissues to be 1475 m/s.

At what speed, in centimeters per second, is the blood moving?

Answer 1

Answer:

V = 2.8cm/s

Explanation:

Please see attachment below.

This problem involves the concept of doppler effect.

Answer 2

Answer:

The speed at which the blood is flowing in cm/s = 1.4 cm/s

Explanation:

emitted frequency ( f ) = 1.1 * 10^6 Hz

detected frequency ( F ) = 21 Hz

speed of sound in tissues ( c ) = 1475 m/s

speed ( V ) = ?

To calculate for speed of blood flowing we apply the detected frequency formula :

F = $\frac{2fV}{c}$

21 = ( 2* 1100000* V ) / 1475

therefore V = (21 * 1475) / (2 * 1100000)

                V = 30975 / 2200000

                 V = 0.0140 m/s = 1.4 cm/sec