Question

A steel pipe has outer radius equal to 3cm and inner radius equal to 2cm. Its length is equal to 5m. What is the mass of the pipe if one cm^3 of steel is 8.05 gram? (Take π = \(\frac{22}{7}\))

(a) 63.25 kg

(b) 65 kg

(c) 67 kg

(d) 61 kg

The question was posed to me in unit test.

I'd like to ask this question from Volume of a Cylinder topic in portion Surface Areas and Volumes of Mathematics – Class 9

Answer 1

Right choice is (a) 63.25 kg

The best I can explain: Let the outer radius = ro = 3cm

Inner radius = ri = 2cm

Height (here length) = l = 5m = 500cm

Volume of pipe = π * (ro ^2 – ri ^2) * l

= \(\frac{22}{7}\) * (3^2 – 2^2) * 500

= 7857.14cm^3

Mass of 1cm^3 is 8.05 gram

Therefore, mass of 7857.14cm^3 is equal to 8.05 * 7857.14

= 63249.97gm

≈ 63250 gm

= 63.25 kg.