Question

The inner and outer radii of a hollow cylinder surmounted on a hollow hemisphere of same radii are 3 cm and 4 cm respectively. If height of the cylinder is 14 cm, then find its total surface area (inner and outer).

Answer 1

• Inner radius (r_inner) = 3 cm
• Outer radius (r_outer) = 4 cm
• Height of cylinder (h) = 14 cm

Outer curved surface area (CSA) = 2πr_outerh = 112π

Inner curved surface area (CSA) = 2πr_innerh = 84π

Surface Areas of Hemisphere

• Outer CSA = 2πr²_outer = 32π
• Inner CSA = 2πr²_inner = 18π

Top Circular Ring Area

Top area = `π(r_(outer)^2 - r_("inner")^2) = 7pi`

Total Surface Area

(112π + 84π) + (32π + 18π) + 7π = 253π

253 × 3.1416

= 794.82 cm²