The floating pencil displaces 5 cm³ of water. What is the weight of the pencil in the air?

V = 5 cm ^ 3 = 5 * 10 ^ -6 m ^ 3.
g = 9.8 m / s ^ 2.
ρ = 1000 kg / m ^ 3.
R – ?
The weight of a body in the air is determined by the formula: P = m * g, where m is the mass of the body, g is the acceleration of gravity.
Two forces act on the floating pencil: the force of gravity m * g and the buoyancy force of Archimedes Farch. Since the pencil floats, these forces are equal to each other.
m * g = Farch.
The buoyancy force of Archimedes is determined by the formula: Farch = ρ * g * V.
Where ρ is the density of the fluid in which the body is immersed, g is the acceleration of gravity, V is the volume of the immersed part of the body in the fluid.
The volume V of the immersed part of the body in the liquid is equal to the volume of water displaced by the pencil.
m * g = ρ * g * V.
P = ρ * g * V.
P = 1000 kg / m ^ 3 * 9.8 m / s ^ 2 * 5 * 10 ^ -6 m ^ 3 = 0.05 N.
Answer: the weight of the pencil in the air is P = 0.05 N.