# Pressure at different heights

ana111790

## Homework Statement

An average man is 5'9" (1.75 m) tall and his heart is 4'4" (1.32 m) above the ground. If the mean arterial blood pressure at the level of the heart is 91mmHg (12103 Pa) and the density of blood is given as 1.056*10^3 kg/m^3.
a) What is the blood pressure in the man's feet in Pa? In the brain when he is standing up tall?
b) The person now lies down so that his feet and brain are at the same height. When his body returns to hydrostatic equilibrium the mean arterial blood pressure remains the same as above. What is the blood pressure in the feet and brain when he is lying down>

## Homework Equations

P = rho*g*h (Pascal's principle)

## The Attempt at a Solution

I am not sure what the signs should be but for part a)
P = P heart + rho*g*h (where h is the height from the heart to the feet)
P = 12103 + (1.056*10^3) * (9.8) * (1.32 m)
P = 25763 Pa
and
P = P heart + rho*g*h (where h is the height from the heart to the brain)
P = 12103 + (1.056*10^3) * (9.8) * (1.75 m)
P = 30213 Pa

Is this correct at all? I am not sure how to approach part B.
Thanks for any help!

## Answers and Replies

Homework Helper
The first calc looks great.
In the second, shouldn't the height difference from heart to head be 1.75 - 1.32? And the second term should be negative; the pressure at the head is less than at the heart.

ana111790
Thank you for your help!!