A lead pencil consists of a cylinder of wood with a solid cylinder of graphite filled in the interior. The diameter of the pencil is 7 mm and the diameter of the graphite is 1 mm. If the length of the pencil is 14 cm, find the volume of the wood and that of the graphite


Radius (pencil), r1 = mm = 0.35 cm

Radius (graphite), r2 = mm = 0.05 cm


Height (Pencil), h = 14 cm


Volume of wood in pencil = π (r12 – r22) h


= [(0.35)2 – (0.05)2 * 14]


= (0.1225 – 0.0025) * 14


= 44 * 0.12


= 5.28 cm3


Volume of graphite = πr22h


= * (0.05)2 * 14


= 44 * 0.0025


= 0.11 cm3


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