Determining recoil velocity?

Question

I was given this physics problem but I'm not too sure on how to approach it. It reads:

For tests using a ballistocardiograph, a patient lies on a horizontal platform that is supported on jets of air. Because of the air jets, the friction impeding the horizontal motion of the platform is negligible. Each time the heart beats, blood is pushed out of the heart in a direction that is nearly parallel to the platform. Since momentum must be conserved, the body and the platform recoil, and this recoil can be detected to provide information about the heart. For each beat, suppose that .050 kg of blood is pushed out of the heart with a velocity of +.25 m/s and that the mass of the patient and platform is 85 kg. Assuming that the patient does not slip with respect to the platform, and that the patient and the platform start from rest, determine the recoil and velocity.

Thanks to anyone who attempts this. I'm really stumped and any explanations, tips, and details will be a great help!

Answer 1

remember Newton? every action has an equal and opposite reaction...
so when your heart pumps blood one way, it pushes the rest of you the other!!!
clearly theres a small amount of blood being pushed, and a whole lot of you, so you will move MUCH slower in the other direction.
so when .050Kg of blood gets pushed at a velocity of 0.25m/s 85Kg will get pushed at a correspondingly smaller velocity.
to calculate...
0.050Kg x 0.25m/s = 0.0125Kgm/s
85Kg x ?m/s = 0.0125Kgm/s
so ? = 0.0125Kgm/s / 85Kg
= 0.000147 m/s (ish)

hope this is clear enough??

Answer 2

The momentum of the blood is p = 0.05*0.25 kg/ms
The platform and patient recoil by conservation of momentum with a speed

v = p/M where M = 85 kg

v = 0.05*0.25/85 = 0.025/17 m/s

Answer 3

one tip to get this right, drop the class and change your major..............