Question

    A metallic sphere of radius 4.2 cms. Is melted and

    recast into the shape of a cylinder of radius 6 cms. Height of the resultant cylinder would be:
    A 110 cms Correct Answer Incorrect Answer
    B 3.84 cms Correct Answer Incorrect Answer
    C 30 cms Correct Answer Incorrect Answer
    D 2.74 cms Correct Answer Incorrect Answer

    Solution

    As a metallic sphere is melted and recast into the shape of a cylinder, their volume must be the same. Volume of the sphere = Volume of the cylinder Let us find the volume of the sphere and cylinder by using formulae; Volume of the sphere = 4/3πr3 where r is the radius of the sphere Volume of the cylinder = πr2h where r and h are radius and height of the cylinder respectively Radius of the sphere, r₁ = 4.2 cm Radius of the cylinder, r₂ = 6 cm Let the height of the cylinder be h. Volume of sphere = Volume of cylinder 4/3πr₁3 = πr₂2h (4/3)r₁3 = r₂2h h = 4r₁3 / 3r₂2 = (4 × 4.2 cm × 4.2 cm × 4.2 cm) / (3 × 6 cm × 6 cm) = 2.744 cm Hence, the height of the cylinder so formed will be 2.744 cm.

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