A spherical ball of diameter 8 cm is cut into two equal parts. The curved area of one such part has to be painted with green colour, while the other part has to be painted with red colour. The bases of both the hemispheres are to be painted with blue colour. The cost of painting with blue is ₹2/cm², while the cost of painting the curved area is ₹3/cm². What will be the cost (in) of painting the hemispheres? (Take π= 3.14)
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. ₹803.84
Radius of ball r = 4 cm (since diameter = 8 cm)
Each hemisphere CSA = 2πr2 = 2 × 3.14 × 16 =100.48
2 hemispheres:
Total CSA = 2 × 100.48 =200.96 cm2
⇒ Cost = 200.96 × 3 = ₹602.88
Each base area= πr2 = 3.14 × 16 = 50.24
2 hemispheres:
Total base area = 2 × 50.24 =100.48 cm2
⇒ Cost = 100.48 × 2 = ₹200.96
Total cost = ₹602.88 + ₹200.96 = ₹803.84