Volume Of Cylinder

Chapter 13 Class 9 Surface Areas and Volumes
Concept wise

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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·πππππ‘ππ ππ ππππβππ‘π)/2 = 1/2 ππ = 1/2 Γ 1/10 cm = 1/20 cm Height of graphite = h = 14 cm Volume of the graphite cylinder = Οr2h = (22/7Γ1/20Γ1/20Γ140) mm3 = (22Γ1/1Γ1/20Γ20) 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·πππππ‘ππ ππ ππππππ)/2 = 7/2 ππ = 7/2 Γ 1/10 cm = 7/20 cm Height of pencil = h = 14 cm Volume of the pencil = Οr2h = (22/7Γ7/20Γ7/20Γ140) mm3 = 5.39 cm3 Volume of wood = Volume of pencil β Volume of graphite = 5.39 β 0.11 cm3 = 5. 28 cm3