# The copper ball weighs 1.78 N in air, and when fully immersed in kerosene, it weighs 1.42 N.

The copper ball weighs 1.78 N in air, and when fully immersed in kerosene, it weighs 1.42 N. Find the volume of the cavity inside the ball. The density of kerosene is 800 kg / m3, the density of copper is 8900 kg / m3.

Given: P1 (ball weight in air) = 1.78 N; P2 (weight in kerosene) = 1.42 N.

Constants: ρк (kerosene density) – 800 kg / m3; ρm (copper density) = 8900 kg / m3; g (acceleration due to gravity) ≈ 10 m / s2.

1) The volume of pure copper: P1 = m * g = ρm * V1 * g; ρm = P1 / (ρm * g) = 1.78 / (8900 * 10) = 2 * 10 ^ -5 m3.

2) The total volume of the ball: Fa = P1 – P2 = ρк * g * V; V = (P1 – P2) / (ρк * g) = (1.78 – 1.42) / (800 * 10) = 4.5 * 10 ^ -5 m3.

3) Cavity volume: V2 = V – V1 = 4.5 * 10 ^ -5 – 2 * 10 ^ -5 = 2.5 * 10 ^ -5 m3 (25 cm3).

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