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Pressure difference when height changes

  • #1

Homework Statement



Calculate the difference in pressure (in atmospheres) that the blood vessels in a giraffe's head have to accommodate as the head is lowered from a full upright position to ground level for a drink. The height of an average giraffe is about 6m.
(Note I'm currently only looking for the answer is Pascals)


Homework Equations



I thought the equation was P=Po + pgh
but the answer just says P=pgh

Po= 101000Pa

The Attempt at a Solution



P=Po + pgh
P=101000 + (1.05x10^3 kg/m^3) x 9.8 x 6m
P=162.740Pa

But the answer gives...

ΔP=pgΔh
[itex]\frac{ΔP}{Po}[/itex] = [itex]\frac{pgΔh}{Po}[/itex]
= [itex]\frac{(1.05\times103)\times9.8\times6}{1.013\times105}[/itex]
=0.609Pa

I don't understand why they've rearranged the equation the way they have and exactly how they are using it. It just doesn't seem right.
Can someone please explain?
 

Answers and Replies

  • #2
747
36
I thought the equation was P=Po + pgh

I don't think so. this is the equation for absolute pressure.
The problem asks for difference in pressure.
 

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