Ultrasound reflected from an oncoming bloodstream that is moving at 31.1 cm/s is

Question

Ultrasound reflected from an oncoming bloodstream that is moving at 31.1 cm/s is mixed with the original frequency of 2.41 MHz to produce beats. Use the speed of sound in human tissue as 1540 m/s. Assume that the frequency of 2.41 MHz is accurate to seven significant figures. (Hint: compare to Example 17.8 in OpenStax College Physics.)

What frequency does the blood receive? (Give an answer in MHz, to 7 significant figures.)

    MHz

What frequency returns to the source? (Give an answer in MHz, to 7 significant figures.)

    MHz

What beat frequency is produced if the source and returning frequencies are mixed? (Give an answer in Hz, to 3 significant figures.)

    Hz

Explanation / Answer

f(observed) = f(s) x (Vw +/- Vw /Vs)

a) (2,410,000 Hz)(1540 m/s + 0.311 m/s) / 1540 m/s) = 2410449.136 Hz = 2.410486 MHz

b) (2410486 Hz)(1540 / 1540 - 0.311) = 2410948.313 Hz = 2.410973 MHz

c) 2410973 - 2410000 = 973Hz

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