How Does Water Pressure Change with Depth and Altitude?

[Devin Longo]

Homework Statement

At the surface of a freshwater lake the pressure is 106 kPa. (a) What is the pressure increase in going 34.5 m below the surface? (b) What is the approximate pressure decrease in going 36 m above the surface? Air at 20°C has density of 1.2 kg/m3.

Homework Equations

Ph20 = pgh
Pabs = Ph20 + Patm

The Attempt at a Solution

I calculated both equations and got 439.4 kPa. I then subtracted 106 from 439.4 to get number one, but it doesn't work! How can I calculate number one? Also, I don't know where to begin for 2!

 

[Doc Al]

The pressure change in both cases can be calculated via ΔP = ρgΔh.