Atmospheric pressure is $1.01\times {10}^5$ pascal. How much force is exerted by the air on a window plane that is $40\text{cm}\times 100\text{cm}$ in size?

Given:
$\text{Pressure}=1.01\times {10}^5\text{Pa}$ 
$\text{Area of the window plane}=(40\times 100){\text{cm}}^{\text{2}}$$=4000{\text{cm}}^{\text{2}}$
We need to convert the area in m² as the pressure is given in SI unit Pascal.
$\mathrm{Area} \mathrm{in} \mathrm{SI} \mathrm{unit}=4000\times {10}^{-4}{\text{m}}^{\text{2}}$$=0.4{\text{m}}^{\text{2}}$

To find: Force

Formula:
$Pressure=\frac{ Force}{Area}$

Solution:
We can arrange the formula of pressure to find the value of the force exerted as follows:
$\text{F}=\text{P}\times \text{A}$
$\mathrm{F}=1.01\times {10}^5\times 0.4$
$\mathrm{F}=0.404\times {10}^5\text{N}$
$\text{F}=\text{4}\text{.04}\times {\text{10}}^4\text{N}$

Therefore, option B is the correct answer.