- #1

dcramps

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## Homework Statement

In an aortic aneurysm, a bulge forms where the walls of the aorta are weakened. If blood flowing through the aorta (radius 1.0cm) enters an aneurysm with a radius of 3.0cm, how much on average is the blood pressure higher inside the aneurysm than the pressure in the unenlarged part of the aorta? The average flow rate through the aorta is 120cm³/s. Assume the blood is nonviscous and the patient is lying down so there is no change in height.

## Homework Equations

Bernoulli's Principle?

P

_{1}+ 1/2pv

_{1}² = P

_{2}+ 1/2pv

_{2}² where:

P

_{1}= pressure in the aorta?

P

_{2}= pressure in the aneurysm?

p = density of blood

v

_{1}= initial velocity

v

_{2}= final velocity

v = flowrate/pi*r²

## The Attempt at a Solution

Calculated the initial velocity to be 38.19718634cm/s

So, using Bernoulli's Principle:

P

_{1}+ 1/2pv

_{1}² = P

_{2}+ 1/2pv

_{2}²

I changed it around a bit:

P1 - P2 = 1/2pv

_{2}² - 1/2pv

_{1}²

ΔP = 1/2pv

_{2}² - 1/2pv

_{1}²

and ended up with:

ΔP = 1/2p(v

_{2}² - v

_{1}²)

But, there is no density for blood given, and I'm unsure what to do about that. Did I make a mistake when I modified the formula?

I am quite confused now. Do I just make up a value for blood density?