Question

An air tight container having a lid with negligible mass and a area of $8c{m}^2$ is partially evacuated . If a 40N force is require to pull a lid off the container and the atmospheric pressure is $1.0\times {10}^{5}Ps$ ,the presure in the container before it is opened must be

• A. 0.6atm
• B. 0.5atm
• C. 0.4atn
• D. 0.2atm

Answer 1

The correct option is C 0.4atn

The pressure inside the container must be equal to the pressure developed by force applied and the atmospheric force would oppose the pull,

So,

$P_{external}=P_{inside}+P_{atmosphere}$

$=\frac{48}{0.008}=P_{inside}+1\times {10}^5$

$P_{inside}=0.6\times {10}^5-1\times {10}^5$

$P_{inside}=-0.4\times {10}^{5}Ps=0.4atm$