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