Question

An airtight box, having a lid of area $80c{m}^2$, is partially evacuated (i.e., has low pressure than outside atmosphere). Atmosphere pressure is $1.01\times {10}^{5}Pa$. A force of $600N$ is required to pull the lid off the box. What was the pressure in the box?

Answer 1

let the force required to open the lid be $F$ and pressure $P$

$P=\frac{F}{A}$

A is given as $80c{m}^2=80\times {10}^{-4}{m}^2$

$P_f=\frac{600}{80\times {10}^{-4}}=7.5\times {10}^{4}Pa$

$P_f=P_a-P_i$

$P_i=P_a-P_f=10.1\times {10}^4-7.5\times {10}^4=2.6\times {10}^{4}Pa$