The stone weighs 50 N. in the air and 20 N. when fully immersed in water.

The stone weighs 50 N. in the air and 20 N. when fully immersed in water. Determine the weight of the displaced water, the volume of the stone and its density.

A stone in water is acted upon by the force of Archimedes and the force of gravity. These forces are exactly the opposite.
The force of Archimedes is equal to the weight of the displaced liquid:
Pv = Ft1 – Ft2, where Ft1 = 50 N, Ft2 = 20 N.
Рв = 50 – 30 = 30 Н = Fа.
Archimedes force: Fa = ρ * g * V, where ρ is the density of water (ρ = 1000 kg / m ^ 3), g is the acceleration of gravity (g = 10 m / s ^ 2), V is the volume of the stone (m ^ 3).
V = Fa / (ρ * g) = 30 / (1000 * 10) = 0.003 m ^ 3.
Density of the stone: ρ = m / V, where m is the mass of the stone (m = Fт1 / g = 50/10 = 5 kg).
ρ = m / V = 5 / 0.003 = 1667 kg / m ^ 3.