Question

a hollow iron pipe is 21 cm long &its external diameter is 8 cm. if the thickness of the pipe is 1 cm and iron weighs 8g/cm cubic units,then the weight of the pipe is

Answer 1

External Diameter=8cm , External radius=4cm

As thickness of the pipe is given as 1cm so internal radius=4-1 = 3 cm

Volume of iron= πr^2h = 22/7{4^2 - 3^2}21 = 22/7*1*21 =462 cm^3

weight of iron= 462*8 =3696 gram or 3.696 kg

Answer 2

Thickness of the pipe is 1cm so internal radius=4-1 = 3 cm

Volume of iron = πr^2h 

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

                        = 22/7*1*21 

                        =462 cm^3

Weight of iron= 462*8 =3696 gram