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# Class 9 RD SHARMA Solutions Maths Chapter 21 - Surface Areas and Volume of a Sphere

## Surface Areas and Volume of A Sphere Exercise Ex. 21.2

### Solution 22

Inner radius (r1) of hemispherical tank  = 1 m
Thickness of hemispherical tank       = 1 cm = 0.01 m
Outer radius (r2) of hemispherical tank = (1 + 0.01) m = 1.01 m
Volume of iron used to make the tank  =

### Solution 23

Volume of spherical capsule

Thus, approximately 22.46 mm3 of medicine is required to fill the capsule.

### Solution 24

Let diameter of earth be d. So, radius earth will be  .
Then, diameter of moon will be  . So, radius of moon will be  .
Volume of moon =
Volume of earth =

Thus, the volume of moon is  of volume of earth.

## Surface Areas and Volume of a Sphere Exercise 21.26

### Solution 1

Sphere has only one surface i.e. curved surface, so number of faces = 1

Hence, correct option is (a).

### Solution 2

A hemisphere has two surfaces: one top surface and other curved surface.

T.S.A. = 2∏r2 + (∏r2)   {Area of Top-face = ∏r2}

= 3∏r2

## Surface Areas and Volume of a Sphere Exercise 21.27

### Solution 12

Sphere touches cylinder at Top, Base and Lateral Surface.

Then,

2r = height of cylinder = h

Volume of cylinder = ∏r2h

=∏r2(2r)

= 2∏r3

Hence, correct option is (c).