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a hollow iron pipe is 21cm long and its external diameter is 8cm. if the thickness of the pipe is 1 cm and iron weigth is 8 g/cm3 then the weigth of the pipe is?
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Mass   =    Density * Volume of the hollow cylinder

=    8 * pi * h * (r22  -   r12)

=    8 * (22/7) * 21 (42 - 32)     [ As outer diameter = 8 cm so radius = 4 cm and as thickness of pipe = 1 cm so inner                                                                 radius = 3 cm ]

=    8 * 22 * 3 * 7

=    3.696 kg

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