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Exercise

A steel pipe is 35.0 cm long and has an inside radius of 8.0 cm and an outside radius of 10.0 cm. How much steel is needed to build the pipe? (The density of steel is about 7.8 g/cm3)

Solution

Given:

            Inner radius r1 = 8.0 cm
            Outer radius r2 = 10.0 cm
            Steel pipe length h = 35.0 cm

The volume of the pipe is the difference of two cylinders: one with the radius of 10.0 cm and the other one with the radius of 8.0 cm. That is,

            V = Imager22h - Imager12h
                = 3.14 × 10.02 × 35.0 - 3.14 × 8.02 × 35.0
                = 3956.4 cm3

The weight of the pipe:

            w = (V) × (density) = 30859.9 (g)
            or approximately 30.86 (kg)


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