Question

The diameter of a metallic ball is 4.2cm.What is the mass of the ball, if density of the metal is8.9gm per cm cube

Answer 1

Density = mass / volume
Or
Mass = density * volume

Here density = 8.9cm³
And,
Volume =
4/3 * 22/7 * 4.2/2 * 4.2/2 * 4.2/2
= 38.808cm³

So,
Mass = 8.9 * 38.808 = 345. 3912kg

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Answer 2

The diameter = 4.2 cm
radius, r = 4.2/2 = 2.1 cm
volume = $\dfrac43 \pi r^3$
= $\dfrac43 \times 3.14 \times 2.1^3$
= 38.77 cm cube

Mass = 38.77 × 8.9 = 345.053 g

As, Mass = Volume × Density