Question

The internal and external diameters of a hollow hemi-spherical vessel are 21 cm and 28 cm respectively. Find: total surface area.

Answer 1

External radius (R) = 14 cm 

Internal radius (r) =`21/2` cm 

Total surface area = 

`2piR^2+2pir^2+pi(R^2-r^2)` 

= `693+1232+22/7((14)^2-(21/2)^2)` 

=`1925+22/7(196-441/4)` 

`=1925+22/7xx343/4`

= 1925 + 269.5

= 2194.5 cm²