The Doppler effect is used in hospitals to measure the rate of blood flow by bouncing ultrasound waves off red blood cells. A pocket Doppler Ultrasound machine is shown below.

i) If the blood flow is away from the emitter, will the frequency received by the red blood cells be higher or lower than the emitted frequency? What if they were moving towards the emitter? ii)Will the frequency measured at the detector (attached to the emitter) be higher or lower? A source with a frequency of 5 x 10^6 Hz is used to measure a patient's blood flowrate. The speed of sound in blood is 1570 m.s^-1. iii)If the average frequency difference between the received and transmitted waves is 140 Hz, what is the velocity of the blood? iv)Given this average blood velocity, how is it possible that the pulse pressure wave produced by the heart reaches the feet in less than 1 s?