Ultrasound in Medicine: A 200 MHz sound wave travels through a pregnant woman's abdomen and is reflected form the fetal heart wall of her unborn baby. the heart wall is moving towards the sound receiver a the heart beats. The reflected sound is then mixed with the transmitted sound and 85 beats per second are detected. The speed of sound in body tissue is 1500 m/s. Calculate the speed of the fetal heart wall at the instant this measurement is made.