What are the different way for solving the question for class 9^{th} question of Surface Areas and Volumes chapter of math of question no.7 of math please suggest me the best way for solving this question of exercise 13.6 A lead pencil consists of a cylinder of wood with solid cylinder of graphite filled in the interior. The diameter of the pencil is 7 mm and the diameter of the is 1 mm. If the length of the pencil is 14 cm, find the volume of the wood and that of the graphite. (Assume π = 22/7)

bhagwansinghGuru

# A lead pencil consists of a cylinder of wood with solid cylinder of graphite filled in the interior. The diameter of the pencil is 7 mm and the diameter of the is 1 mm. If the length of the pencil is 14 cm, find the volume of the wood and that of the graphite. (Assume π = 22/7) Q.7

Share

Radius of pencil, r

_{1 }= 7/2 mm = 0.7/2 cm = 0.35 cmRadius of graphite, r

_{2 }= 1/2 mm = 0.1/2 cm = 0.05 cmHeight of pencil, h = 14 cm

Formula to find, volume of wood in pencil = (r

_{1}^{2}-r_{2}^{2})h cubic unitsSubstitute the values, we have

= [(22/7)×(0.35

^{2}-0.05^{2})×14]= 44×0.12

= 5.28

This implies, volume of wood in pencil = 5.28 cm

^{3}Again,

Volume of graphite = r

_{2}^{2}h cubic unitsSubstitute the values, we have

= (22/7)×0.05

^{2}×14= 44×0.0025

= 0.11

So, the volume of graphite is 0.11 cm

^{3}.