Question

A lead pencil consists of a cylinder of wood with a solid cylinder of graphite filled into it. The diameter of the pencil is 7mm, the diameter of the graphite is 1mm and the length of the pencil is 10cm. Calculate the weight of the whole pencil, if the specific gravity of the wood is 0.7gm/cm3 and that of the graphite is 2.1 gm/cm3

Answer 1

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Answer 2

Answer:

Here's your answer

Step-by-step explanation:

Here rp = radius of the pencil

And,rg = radius of graphite

Given:

⇒Radius of pencil =7​/2mm = 3.5mm

⇒0.35cm = rp

⇒h = 10cm,

⇒Volume of wood in pencil = π (r^2p​ − r^2g​) h

⇒22/7 ​[(0.35)^2 − (0.05)^2] 10

⇒22/7​ (0.1225−0.0025) × 10

⇒3.14×1.2

= 3.768cm^3

Volume of a graphite = πr^2g​h

⇒22/7​ × (0.05)^2 × 10cm^3

⇒3.14 × 0.0025cm^3 ×1000

⇒7.85cm^3

Hope you understand.