Question

-5.
(C) 550 cm
(D) 560 cm
Radius and height of a cylinder are 7 cm and 14 cm respectively. It is divided along its axis vertically
into equal parts. The increase in its total surface area is :
(A) 392 sq. cm
(B) 308 sq. cm
(C) 196 sq. cm
(D) 154 sq. cm



please give correct answer.
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Answer 1

Answer:

Surface area of a cylinder is 2×pi×r×(r+h). So the surface area of a cylinder with radius 5 cm and height 16 cm will be

2×22/7×5×(5+16) = 220/7×(21) = 220×3 = 660 square centimetres.

When cylinder is cut vertically into 2 equal parts, surface areas of 2 rectangular faces will be added into total surface area. When cylinder is cut vertically into 2 equal parts, the length will be it's height and width will be the diameter of circular face. Therefore the area of the 2 rectangular faces will be

2(2r×h) = 2(10×16) = 2×160 = 320 square centimetres

So the total surface area of both the parts will be 660+320 = 980 square centimetres and total surface area of each part will be 980/2 = 490 square centimetres.