m = 2.4 kg.
g = 9.8 m / s ^ 2.
ρp = 245 kg / m ^ 3.
ρw = 1000 kg / m ^ 3.
Two forces act on the circle: the force of gravity m * g, vertically downward and the buoyancy force of Archimedes Farch, vertically upward.
Lift force F will be the difference: F = Farch – m * g.
The buoyancy force of Archimedes is determined by the formula: Farch = ρw * 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.
Find the volume of the life buoy V.
According to the definition, the density is determined by the formula: ρп = m / V.
V = m / ρп.
Farch = ρw * g * m / ρp.
F = ρw * g * m / ρп – m * g.
F = 1000 kg / m ^ 3 * 9.8 m / s ^ 2 * 2.4 kg / 245 kg / m ^ 3 – 2.4 kg * 9.8 m / s ^ 2 = 72.5 N.
Answer: the lifting force of the circle in water F = 72.5 N.
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