When the heart beats it expels a mass m of blood into the aorta with speed v, and the body and platform move in the opposite direction with speed v. The bllod velocity can be determine independently by observing the Doppler shift of ultrasound. Assume that v is 50.0 cm/s in one trial. The mass of the subject plus the platform is 54.0kg. The platform moves 6x10^-5 m in 0.160s after one heart beat. Calculate the mass m of blood that leaves the heart. initially I used the equation m1v1=m2v2 and calculated the mass of blood to be 0.041kg. But I'm not sure if you can use conservation of momentum in this question. A friend of mine used (ma)_body=(ma)_blood and calcualted the mass of the blood to be 0.08kg...but i'm not sure if this makes sense.