Question

The difference between outside and inside surface of a cylindrical metallic pipe 14m long is 44 cm2. If the sum of the diameters of the inner and outer surface of the cylinder is 9 cm, find the inner and outer radii of the cylinder.
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Answer 1

Answer:

Let, R be the external radius and r be the inner radius of the metallic pipe. h=14cm

Outer surface area−inner surface area=44cm2

∴2πRh−2πrh=44cm2

∴R−r=2×722×1444=2×22×1444×7

∴R−r=21.

The volume of metal used =99cm3

∴ External volume − internal volume =99cm3

∴πR2h−πr2h=99cm3

∴πh(R2−r2)=99cm3

∴722×14(R+r)(R−r)=99cm3 [∵a2−b2=(a+b)(a−b)] and [∵R−r=1/2]

22×2(R+r)2

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