Page 4 - Lesson Note-4-Ch-13 SA and Volume(Sphere)

2 r = 17.6

22
 2  r = 17.6
7

17.6 7
 r = = 2.8m

2 22
22
CSA = 2 r =   2.8 2.8m 2


2
2
7
= 49.28m 2
Cost of painting per 100 = Rs 5
2
So, Cost of painting per 1 = Rs. 500
2
2
Total cost of painting for 49.28 = . 500 × 49.28 =Rs. 24640
Example-4

Find the total surface area of a hollow sphere whose external radius is 7 cm with 1
cm thickness. (π = 3.14)

Solution

Given, R = 7 cm, Thickness (R−r)= 1 cm

r = (7−6) cm= 1 (thickness is 1 cm)

Total Surface area = [ ( − ) +2 ( + ) ] sq.unit
2
2
2
2
=  (49 36− ) 2  + (49 36+ )
13 +  = 170 
183=

= (183 3.14)cm 2
= 574.62cm 2
Example-5
Find the volume of a sphere of radius 11.2 cm.
Solution

r = 11.2 cm.
Volume of the sphere
4
=  r 3
3
4 22
3
=   11.2 11.2 11.2cm


3 7
= 5887.32cm 3

4