1. The problem statement, all variables and given/known data A Doppler blood flow unit emits ultrasound at 5.0 MHz. What is the frequency shift of the ultrasound reflected from blood moving in an artery at a speed of 0.20 m/s? Express your answer using two significant figures. 2. Relevant equations f' = f0(v/v-Vs) frequency shift = f' - f0 f0 = 5*10^6 Hz v = 1500 m/s (assumed) Vs = 0.20 m/s 3. The attempt at a solution Plugging in the numbers we get the following equation for frequency shift: (5*10^6)*[1500/(1500-0.2)]-5*10^6 Which comes out to approx 666 Hz. or 6.7 *10^2 Hz using 2 significant figures. However, this problem comes from an online hw set and according to that 6.7 *10^2 is not the correct solution. Does anyone have an idea of what I am doing wrong? Thanks in advance for any and all help!
Hi grigri9, welcome to PF. We have here a case of the "listener" (the blood corpuscles) moving away from a stationary source, and thus the frequency, f corpuscle that will be reflected by the corpuscles will be f corpuscle = f(transmitted)[(Vs - Vb)/Vs For the reflected waves, reflection, the corpuscles are the source and the "listener" is the receiver. The frequency at the receiver will be f(receiver) = f(corpuscles)*Vs/(Vs + Vb) from which we get f(receiver) = f(transmitted)*(Vs-Vb)/(Vs+Vb)