NCERT Solutions
Class 9 - Mathematics - Chapter 11: SURFACE AREAS AND VOLUMES
EXERCISE 11.2

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Question. 1

Find the surface area of a sphere of radius:

(i) 10.5 cm    (ii) 5.6 cm    (iii) 14 cm

Answer:

(i) 1386 cm²    (ii) 394.24 cm²    (iii) 2464 cm²

Question. 2

Find the surface area of a sphere of diameter:

(i) 14 cm    (ii) 21 cm    (iii) 3.5 m

Answer:

(i) 616 cm²    (ii) 1386 cm²    (iii) 38.5 m²

Question. 3

Find the total surface area of a hemisphere of radius 10 cm. (Use π = 3.14)

Answer:

942 cm²

Question. 4

The radius of a spherical balloon increases from 7 cm to 14 cm as air is being pumped into it. Find the ratio of surface areas of the balloon in the two cases.

Answer:

1 : 4

Question. 5

A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of tin-plating it on the inside at the rate of ₹16 per 100 cm².

Answer:

₹27.72

Question. 6

Find the radius of a sphere whose surface area is 154 cm².

Answer:

3.5 cm

Question. 7

The diameter of the moon is approximately one fourth of the diameter of the earth. Find the ratio of their surface areas.

Answer:

1 : 16

Question. 8

A hemispherical bowl is made of steel, 0.25 cm thick. The inner radius of the bowl is 5 cm. Find the outer curved surface area of the bowl.

Answer:

173.25 cm²

Question. 9

A right circular cylinder just encloses a sphere of radius r. Find:

(i) surface area of the sphere

(ii) curved surface area of the cylinder

(iii) ratio of the areas obtained in (i) and (ii)

Answer:

(i) 4πr²    (ii) 4πr²    (iii) 1 : 1