# The cast iron ball has a mass of 4.2 kg with a volume of 700 cm3. Determine if this ball has a cavity inside.

m = 4.2 kg.

V = 700 cm ^ 3 = 0.0007 m ^ 3

ρ = 7000 kg / m ^ 3.

Vп -?

According to the definition, the density of a substance ρ is the ratio of its mass m to its volume V: ρ = m / V.

Let us express the volume of the sphere from the formula: V = m / ρ.

We find the density of cast iron ρ from the table of the density of substances ρ = 7000 kg / m ^ 3.

V1 = 4.2 kg / 7000 kg / m ^ 3 = 0.0006 m ^ 3.

Since V1 <V, it means that there is a void in the ball.

The volume of the void is found by the formula: Vp = V – V1.

Vp = 0.0007 m ^ 3 – 0.0006 m ^ 3 = 0.0001 m ^ 3.

Answer: the ball has a void with a volume of Vp = 0.0001 m ^ 3.

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