Q. 145.0( 6 Votes )

# A lead pencil con

Answer : Concept Used: Volume of the wood = Volume of a pencil – volume graphite

Volume of Cylinder = πr2h

Where r = radius of the cylinder and h = height of the cylinder

Given: Diameter of pencil = 7 mm

Diameter of graphite = 1 mm

Length of the pencil = 14 cm

Assumption: Let r1 be the radius of pencil, r2 be the radius of graphite and h be the height of pencil.

Explanation:

Radius 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

Hence, The volume of wood in pencil is 5.28 cm3 and volume of graphite in pencil is 0.11 cm3.

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