Question

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.​

Answer 1

Answer:

⇒Radius of pencil =

2

7

​

mm=3.5mm

⇒0.35cm =r

p

​

⇒h=14cm,

Radius of graphite =

2

1

​

mm=0.05cm

⇒Volume of wood in pencil =π(r

p

2

​

−r

g

2

​

)h

⇒

7

22

​

[(0.35)

2

−(0.05)

2

]14

⇒

7

22

​

(0.1225−0.0025)×14

⇒44×0.12=5.28cm

3

⇒Volume of a graphite =πr

g

2

​

h

⇒

7

22

​

×(0.05)

2

×14cm

3

⇒44×0.0025cm

3

⇒0.11cm

3

Answer 2

Answer:

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