Ex13.6 ,7
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.
Volume of graphite
Graphite is in shape of cylinder with
Radius of graphite = r = (π·πππππ‘ππ ππ ππππβππ‘π)/2 = 1/2 ππ
= 1/2 Γ 1/10 cm = 1/20 cm
Height of graphite = h = 14 cm
Volume of the graphite cylinder = Οr2h
= (22/7Γ1/20Γ1/20Γ140) mm3
= (22Γ1/1Γ1/20Γ20) mm3
= 0.11 cm3
Volume of wood
Volume of wood = Volume of pencil β Volume of graphite
Calculating Volume of the pencil
Radius of pencil = r = (π·πππππ‘ππ ππ ππππππ)/2 = 7/2 ππ
= 7/2 Γ 1/10 cm = 7/20 cm
Height of pencil = h = 14 cm
Volume of the pencil = Οr2h
= (22/7Γ7/20Γ7/20Γ140) mm3
= 5.39 cm3
Volume of wood = Volume of pencil β Volume of graphite
= 5.39 β 0.11 cm3
= 5. 28 cm3

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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