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