Concept:
Absolute pressure: The pressure measured above absolute zero (or complete vacuum) is known as Absolute pressure.
Absolute Pressure = Atmospheric pressure + Gauge pressure
Absolute Pressure = Atmospheric pressure – Vaccum pressure
Calculation:
Given,
Atmospheric pressure = 91 kPa
Depth of lake = 60 m
Unit weight of lake water (γ) = 9790 N/m3
Gauge pressure at the bottom of lake = ρgh = γh = 9790 × 60 × 10-3 = 587.4 kPa
Absolute pressure at the bottom of the lake (Pabs) = Atmospheric pressure + Gauge pressure
Pabs = 91 + 587.4 = 678.4 kPa