1. A wooden bowl is in shape of a hollow hemisphere of internal radius 8 cm and thickness 1 cm. Find the total surface area of the bowl?
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By: anil on 05 May 2019 02.15 am
The hemispherical bowl has three surfaces to calculate : the interior hemisphere $$(r_{int} = 8)$$ cm , the exterior hemisphere $$(r_{ext} = 8+1 = 9)$$ cm and the annular(ring shaped) top edge $$(r_{ext} , r_{int})$$ Area of hemisphere = $$2 pi r^2$$ and area of annular = $$pi (r^2_{ext} - r^2{int})$$ Total surface area of hemisphere is the sum of these 3 areas = $$[2 pi (8)^2] + [2 pi (9)^2] + [pi (9^2 - 8^2)]$$ = $$pi [(2 imes64) + (2 imes81) + (81 - 64)]$$ = $$pi(128 + 162 + 17) = 307 pi$$ = $$307 imes frac{22}{7} = 964.85$$ $$cm^2$$ => Ans - (A)
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