A Doppler unit that measures blood flow emits 4.8 MHz ultrasound. The ultrasound waves reflect from blood flowing through an artery that makes a 25 angle with the ultrasound beam as shown in the figure. The blood is moving towards the probe at 1.3 m/s. What is the frequency shift of the reflected ultrasound? Enter a positive value if the received frequency is higher than the emitted frequency, and a negative value if the received frequency is lower than the emitted frequency. Speed of sound in human tissue is 1540 m/s. Ultrasound transducer I Human tissue v=1.3 m/s