## Curved Surface Area Solution7

In this page curved surface area solution7 we are going to see solution of some practice questions.

Question 14

The central angle and radius of a sector of a circular disc are 180 degree and 21 cm respectively. If the edges of the sector are joined together to make a hollow cone,then find the radius of the cone.

Solution:

Solution:

The cone is being created by joining the radius. So the radius of the sector is going to be the slant height of the cone.

Slant height (L) = 21 cm

Arc length of the sector = Circumference of the base of the cone

Length of arc = (θ/360) x 2Π R

Here R represents radius of the sector

= (180/360) x 2 x (22/7)x (21)

= (1/2) x 2 x 22x 3

=  66 cm

So,circumference of the base of the cone = 66

2 Π r = 66

2 x (22/7) x r = 66

r = 66 x (1/2) x (7/22)

r = 10.5 cm

Radius of the cone = 10.5 cm

Question 15

Radius and slant height of a solid right circular cone are in the ratio 3:5. If the curved surface area is 60 Π cm², then find its total surface area.

Solution:

Radius and slant height of a solid right circular cone are in the ratio 3:5.

r : L = 3 : 5

r/L =3/5

r = 3L/5

Curved surface area of cone = 60 Π cm²

Π r L = 60 Π

Π x (3L/5) x L = 60 Π

L² = 60 Π x (1/Π) x (5/3)

L² = 60 x (5/3)

L² = 100

L = 10

r = 3(10)/5

r = 6

Total surface area = Π r (L + r)

= Π (6) (10 + 6)

= 96 Π cm²

Total surface area of cone = 96 Π cm²

curved surface area solution7 curved surface area solution7