A lead pencil consists of a cylinder of wood with a solid cylinder of graphite fitted into it. The diameter of the pencil is 7 mm, the diameter of the graphite is 1 mm and the length of the pencil is 10 cm. calculate the weight of the whole pencil, if the specific gravity of the wood is 
and that of the graphite is 
Given,
Diameter of pencil = 7 mm
Radius of pencil = 
Diameter of graphite = 1 mm
Radius of graphite = 
Volume of graphite = πr2h = 
Weight of graphite = volume × specific gravity of graphite
= 
Volume of wood = volume of pencil – volume of graphite
= 
= 
∴ Total weight of the pencil = weight of wood + weight of graphite
= 0.165 + 2.64 = 2.805 g.
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