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
11