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Fundamentals Of Physics
Found in: Page 407

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Short Answer

Giraffe bending to drink. In a giraffe with its head 2.0 m above its heart, and its heart 2.0 m above its feet, the (hydrostatic) gauge pressure in the blood at its heart is250 torr. Assume that the giraffe stands upright and the blood density is 1.06×103kg/m3 . (a) In torr (or role="math" localid="1657260976786" mm Hg), find the (gauge) blood pressure at the brain (the pressure is enough to perfuse the brain with blood, to keep the giraffe from fainting). (b) torr In (or mm Hg), find the (gauge) blood pressure at the feet (the pressure must be countered by tight-fitting skin acting like a pressure stocking). (c) If the giraffe were to lower its head to drink from a pond without splaying its legs and moving slowly, what would be the increase in the blood pressure in the brain? (Such action would probably be lethal.)

  1. Gauge pressure at the brain of giraffe is 94 torr
  2. Gauge pressure at the feet of giraffe is 406 torr
  3. Increment in pressure is 312 torr
See the step by step solution

Step by Step Solution

The given data

  1. Density of blood, p=1.06×103kg/m3
  2. Heart pressure, p=250torr

Understanding the concept of gauge pressure

Use the formula for gauge pressure, which depends on density, height, and acceleration due to gravity. Gauge pressure is that, which is exerted by a fluid at any point of time at equilibrium due to the force applied by gravity.


Pressure applied on a fluid surface, p=pgh

Net pressure applied on a body, p=p2-p1

a) Calculation of pressure at brain

From equation (ii), the pressure at brain can be given as:

pbrain=pheart-pgh =250-1.06×103×9.8×2×1torr133.33Pa (1torr = 133.33Pa) =94.2torr

The pressure at brain is 94.2 torr.

b) Calculation of pressure at feet

From equation (ii), the pressure at brain can be given as:

Pfeet =Pheart +pgh (here pressure is total pressure) =250+1.06×103×9.8×2×1torr133.33Pa (1torr=133.33Pa) =405.8torr

The pressure at feet is 405.8 torr.

c) Calculation of increment in pressure

From equation (ii), the net pressure between brain and feet can be given as:

p=pbrain-pfeet =405.8-94.2 =311.6torr

Hence, the increased value of pressure is 311.6 torr.

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