Question

An iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm. An iron weighs 8 gram per centimetre cube. Find its weight

Answer 1

given that,
external diameter = 8 cm
external radius = R =4 cm
thickness= 1 cm
so, internal diameter= (8-1) cm = 7 cm
internal radius = r = 3.5 cm

volume of iron = π(R²- r²)h
$= > \frac{22}{7}( {4}^{2} - {3.5}^{2} )21$
=> 247.5 cm³

weight of iron = 247.5× 8 = 1980 gram or 1.98 kg

Answer 2

Let R be outer radius and r be inner radius...

The outer diameter is 8 cm

So R = 8/2 = 4cm

The thickness i.e is the inner diameter from one side is 1cm

r = [8-(1+1)]/2 = 3

=> V = π x (R^2 - r^2) x h

= 22/7 x {(4)^2 - (3)^2} x 21

= 22 x (16 - 9) × 3

= 22 × 7 × 3

= 462cm^3

Density = mass/volume

Mass = d×v

= 10×462

= 4620g

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