Question

Find the pressure exerted by a man weighing $90kg$ on the ground.
(a) when he is standing on one of his feet having an area of $90c{m}^2$.
(b) when he is lying flat. The area of his body in contact with the ground is $0.9m^2$. Given $g=10m{s}^{-2}$.

Answer 1

Force exerted by the man (thrust) $=mg$
$=90kg\times 10m{s}^{-2}=900kgm{s}^{-2}=900N$
(a) pressure exerted by man while standing $=\frac{Force}{Area}$
$=\frac{900N}{\left(\begin{array}{c}\frac{90}{10000}\end{array}\right)m^2}=\frac{900\times 10000}{90}N{m}^{-2}={10}^{5}N{m}^{-2}$
(b) Pressure exerted by man while lying $=\frac{Force}{Area}=\frac{900N}{0.9m^2}=\frac{9000N}{9m^2}=1000N{m}^{-2}$
$={10}^{3}N{m}^{-2}$