When you suddenly stand up after lying down for a while, your body may not compe

Question

When you suddenly stand up after lying down for a while, your body may not compensate quickly enough for the pressure changes and you might feel dizzy for a moment.

(a) If the gauge pressure of the blood at your heart is 14.71 kPa and your body doesn't compensate, what would the pressure be at your head, 60 cm above your heart?

(b) If the gauge pressure of the blood at your heart is 14.71 kPa and your body doesn't compensate, what would it be at your feet, 1.30 102 cm below your heart?Hint: The density of blood is 1060 kg/m3.

Explanation / Answer

given that gauge pressure = 14.71*1000 Pa

generally if we go up the pressure decreases by the formula

P1-P2 = rho*g*h

rho is the density of blood = 1060 kg/m^3

h = 60 cm = 0.6 m
g is the accelaration due to gravity = 9.8 m/s^2

P1 = gauge pressure = 14.71*1000 = 14710 Pa

P2 = P1-(rho*g*h) = 14710-(1060*9.8*0.6) = 8477.2 = 8.477 kPa is the pressure at head

b) at feet and h = 1.3*10^2 cm = 1.3 m

P1 = P2+(rho*g*h) = (14710)+(1060*9.8*1.3) = 28.214 kPa

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