The mass of a boy is 20 kg and the area of the sole of his foot is 0.01m². If g=10m/s^2, then the pressure exerted on the floor when he is standing on one foot is ______.

We have, $\mathrm{Pressure}=\frac{\mathrm{Force}}{\mathrm{Area}}$
Mass of a boy, m = 20 kg
Force, F = mg 

$=20\times 10$ 

$= 200\mathrm{N}$
When the boy is standing on one foot,
The total area of foot, A = 0.01m²
Pressure, $\mathrm{P}=\frac{200 \mathrm{N}}{0.01\mathrm{ }{\mathrm{m}}^2}$ = 20,000N/m²
The pressure exerted on the floor when the boy is standing on one foot is 20,000 N/m².