Question

A lead pencil consists of a cylinder of wood with solid cylinder of graphite filled into it the diameter of pence is 7mm the diameter of the graphite is 1mm and the length of the pencil is 10 cm calculate the weight of whole pencil if the specific gravity of the wood is 0.7g/cm cube that of the graphite is 2.1g/cm cube

Answer 1

radius of graphite , r = 0.5mm = 0.05cm
radius of wooden part of pencil, R = 3.5mm = 0.35cm
length of pencil , l = 10cm

now, volume of graphite = πr²l
= π(0.05)² × 10
= π × 25 × 10^-3 cm³

weight of graphite = π × 25 × 10^-3 × 2.1 g [ mass = volume × density ]
= 22/7 × 25 × 10^-3 × 2.1 g
= 165 × 10^-3 = 0.165g

volume of wooden part of pencil = π(R² - r²)l
= π(0.35² - 0.05²) × 10
= π(0.35 + 0.05)(0.35 - 0.05) × 10
= π × 0.4 × 0.30 × 10
= π × 1.2

weight of wooden part , w = π × 1.2 × 0.7
= 22/7 × 1.2 × 0.7
= 2.64g

so, total weight of pencil = 2.64g + 0.165g
= 2.805g

Answer 2

Step-by-step explanation:

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