A solid brass sphere of radius 21 cm is converted into a right circular cylindrical rod of length 28 cm. The ratio of total surface areas of the rod to sphere is :
Question and options
A solid brass sphere of radius 21 cm is converted into a right circular cylindrical rod of length 28 cm. The ratio of total surface areas of the rod to sphere is :
- 3:1
- 7:6
- 7:3
- 3:7
Answer and explanation
Correct answer: B - 7:6
Volume: (4/3)pi*21^3 = pi*r^2*28 gives r^2 = 441, r = 21. Rod TSA = 2pi*21*(21+28) = 2058pi; sphere = 4pi*441 = 1764pi. Ratio 2058:1764 = 7:6.
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