An airtight box, having a lid of area 12 in2, is partially evacuated. Atmospheric pressure is

Question

15 lb/in2. A force of 108 lb is required to pull the lid off the box. The pressure in the box
was:

Answer 1

The atmospheric force on the top of the lid is 12 x 15 = 180 lb. Subtract 108 for the net force oto the top from above. That equals the force due to inside pressure

180 - 108 = P(inside) * 12 in^2

72 lb = P(inside) * 12

P(inside) = 6 lb/in^2