1.  The volume of a sphere of radius r is obtained by multiplying its surface area by :


43
r3
4r3
3r


Answer

 Option

Volume = 43 πr3 = r3 (4πr2) = r3 * Surface area.

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2.  The curved surface area of a right circular cylinder of base radius r is obtained by multiplying volume by :


2r
2r
2r2
2r2


Answer

 Option

Curved surface are = 2πrh = (πr2h) 2r = (Volume * 2r)

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3.  A hemisphere and a cone have equal bases. If their heights are also equal, then the ratio of their curved surfaces will be :


1 : 2
2 : 1
1 : 2
2 : 1


Answer

 Option

Let the radius of each be R. Height of hemisphere, H = R. So, height of cone = height of hemisphere = R. Slant height of cone = R2 + R2 = 2R. Curved surface area of hemisphereCurved surface area of cone = 2πR2πR * 2R = 2 : 1.

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4.  Surface area of a sphere is 2464 cm2. If its radius be doubled, then the surface area of the new sphere will be :


4928 cm2
9856 cm2
19712 cm2
Data insufficient


Answer

 Option

Let the original radius be r. Then, original surface area = 4πr2 = 2464 cm2 (given) New radius = 2r. New surface area = 4π(2r)2 = 4 * 4πr2 = (4 * 2464) cm2 = 9856 cm2.

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5.  The dimensions of a piece of iron in the shape of a cuboid are 270 cm * 100 cm * 64 cm. If it is melted and recast into a cube. then the surface area of the cube will be :


14400 cm3
44200 cm3
57600 cm3
86400 cm3


Answer

 Option

Volume of the cube = (270 * 100 * 64) cm3. Edge of the cube = 270 * 100 * 64 cm = (3 * 10 * 4) cm = 120 cm. Surface area = (6 * 120 * 120) cm2 = 86400 cm2.

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