Adoppler flow meter is used to measure the speed of blood flow. transmitting and receiving elements are placed on the skin, as shown in the figure below. typical sound-wave frequencies of about 5.0 mhz are used, which have a reasonable chance of being reflected from red blood cells. by measuring the frequency of the reflected waves, which are doppler-shifted because the red blood cells are moving, the speed of the blood flow can be deduced. "normal" blood flow speed is about 0.1 m/s. suppose that an artery is partly constricted, so that the speed of the blood flow is increased, and the flow meter measures a doppler shift of 780 hz.

what is the speed of blood flow in the constricted region? the effective angle between the sound waves (both transmitted and reflected) and the direction of blood flow is 45o, assume the velocity of sound in tissue is 1540 m/s.