Question

a metal pipe is 77 cm long the inner diameter of cross section is 4 cm the outer diameter being 4.4 cm find its curved surface area

Answer 1

Length of pipe = 77 c.m.

Inner diameter = 4 c.m.

Outer diameter = 4.4c.m.

1) Inner curved surface area

          radius = inner diameter  / 2       => 4 c.m./2      => 2 c.m.

      curved surface area = 2 / rh    =>  2* 22 * 77              => 2 *22* 11 = 968 c.m.2

                                                               _____________

                                                                       7

2). Outer curved surface area 

     radius = outer diameter  / 2             =>  4.4 c.m. / 2        => 2.2 c.m.

           curved surface area =  2 / rh  

                     = 2 * 22* 2.2* 77

                 __________________                   =>   1064.8 c.m.2

                                7

3)   total surface area

                Let outer radius be R and inner radius be r

       surface area on the end = 2 / ( R+r )( R -r )

                       = 2 *22 * ( 2.2 + 2) ( 2.2 -2)

                               __

                               7

                  = 2* 22* 4.2 * 0.2

                  ________________                       = 5.28 c.m.2

                           7 

           total surface area = 968 c.m.2 + 1064.8 c.m.2 +5.28 c.m.2 = 2038.08 c.m. 2

Answer 2

22/7*77*4.4*2+2*22/7*4
=4065.6cm²