Assuming that the density of a person is the same as the density of water, what buoyant force does the atmosphere exert on a person whose mass is 70 kg?

the buoyant force F will be 0.84 N

Explanation:

Assuming that a person has the density of water, then its volume could be calculated through

V = m/ρ, where m = mass of the person, ρ = density of water

then

V = m/ρ = 70 kg / 1000 kg/m³ = 0.07 m³

then the buoyant force will be equal to the mass of displaced air in the volume V.

if we assume that the density of air in the atmosphere is ρa=1.225 kg/m³ then the buoyant force F will be

F = ρa*V*g = 0.07 m³*1.225 kg/m³ * 9.8 m/s² = 0.84 N