Question

a hollow cylindrical iron pipe is 21 m long and its outer and inner diameter is 10 cm and 6 cm resptively find the volume iron used in making the pipe also find the outer surface area of pipe

Answer 1

Length=21m=210cm
Outer radius=10/2=5cm
Inner radius=6/2=3cm

Volume of iron used in making
=22/7*210[(5)^2-(3)^2]
=660[25-9]
=660*16
=10560cm

Answer 2

21 m = 2100 cm
h=2100
R=10/3
r=6/2

vol. of R = πR^2h...1
vol. of r =πr^2h...2

vol. of cyl. = 1-2
πR^2h&πr^2h
πh(R^2-r^2)
22/7×2100(R+r)(R-r)
300×8×2
4800cm^3

outer surface area= 2πRh
2×22/7×10×2100
2×22×5×300
=66000cm^2

hope this would help u : )