Surface Area of Right Circular Cylinder,
Surface Area of Hollow Cylinder,
Surface Area of Right Circular Cone,
Surface Area of The Sphere,
Surface Area: Frustum of a right circular cone.
(Maths Book back answers and solution for Exercise questions)

Exercise 7.1

1. The radius and height of a cylinder are in the ratio 5:7 and its curved surface area is 5500 sq.cm. Find its radius and height.

2. A solid iron cylinder has total surface area of 1848 sq.m. Its curved surface area is five – sixth of its total surface area. Find the radius and height of the iron cylinder.

3. The external radius and the length of a hollow wooden log are 16 cm and 13 cm respectively. If its thickness is 4 cm then find its T.S.A.

4. A right angled triangle *PQR* where ∠*Q* = 90 is rotated about *QR* and *PQ*. If *QR*=16* *cm and* PR*=20* *cm, compare the curved surface areas of the right circular* *cones so formed by the triangle.

5. 4 persons live in a conical tent whose slant height is 19 cm. If each person require 22 cm2 of the floor area, then find the height of the tent.

6. A girl wishes to prepare birthday caps in the form of right circular cones for her birthday party, using a sheet of paper whose area is 5720 cm2, how many caps can be made with radius 5 cm and height 12 cm.

7. The ratio of the radii of two right circular cones of same height is 1:3. Find the ratio of their curved surface area when the height of each cone is 3 times the radius of the smaller cone.

8. The radius of a sphere increases by 25%. Find the percentage increase in its surface area.

9. The internal and external diameters of a hollow hemispherical vessel are 20 cm and 28 cm respectively. Find the cost to paint the vessel all over at ₹ 0.14 per cm2 .

10. The frustum shaped outer portion of the table lamp has to be painted including the top part. Find the total cost of painting the lamp if the cost of painting 1 sq.cm is ₹ 2.

Answers:

1. 25 cm, 35 cm

2. 7 m, 35 m

3. 2992 sq.cm

4. CSA of the cone when rotated about PQ is larger.

5. 18.25 cm

6. 28 caps

7. √5 : 9

8. 56.25%

9. ₹ 302.72

10. ₹ 1357.72

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