Question

A laboratory room keeps a vacuum of 4 in. of water due to the exhaust fan. What is the net force on a door of size 6 ft by 3 ft?

Answer 1

The net force on the door is the difference between the forces on the two sides as the pressure times the area

= Poutside A – Pinside A = ∆P × A

= 4 in H2O × 6 ft × 3 ft

= 4 × 0.036126 lbf/in2 × 18 ft2 × 144 in2/ft2

= 374.6 lbf

H2O is 0.036 126 lbf/in2, unit also often listed as psi.