CBSE Class 9 - Maths - Surface Areas and Volumes (NCERT Ex 13.4) (#cbseclass9notes)

Surface Areas and Volumes - Spheres

(NCERT Ex 13.4)

Q1: Find the surface area of a sphere of radius 
(i) 10.5 cm
(ii) 5.6 cm
(iii) 14 cm

Answer:
(i) r = 10.5 cm
Surface area of the sphere = 4πr²
= 4 × (22/7) × (10.5)²
  = 1386 cm² (Answer)

(ii) r = 5.6 cm
Surface area of the sphere = 4πr²
= 4 × (22/7) × (5.6)²
= 394.24 cm² (Answer)

(iii) r = 14 cm
Surface area of the sphere = 4πr²
= 4 × (22/7) × 14 × 14
= 2464 cm² (Answer)


Q2: Find the surface area of sphere of a diameter :
(i) 14 cm
(ii) 21 cm
(iii) 3.5 m

CBSE Class 12 - English (Elective)- Marking Scheme of Sample Question Paper (2016-17)

CBSE Class 12 - English (Elective)- Marking Scheme of Sample Question Paper (2016-17) 


☛See English (Elective) Sample Question Paper (2016-17)

CBSE Class 9 - Maths - Surface Areas and Volumes - NCERT Ex 13.3 (#cbsenotes)

Surface Areas and Volumes

EXERCISE 13.3

Q1: Diameter of the base of a cone is 10.5 cm and its slant height is 10 cm. Find its curved surface area.

Answer: Given r = 10.5/2 = 5.25 cm, l = 10 cm.

Curved surface area (CSA) of the cone = πrl
= (22/7) × 5.25 × 10  = 165 cm² (Answer)



Q2: Find the total surface area of a cone, if its slant height is 21 m and diameter of its base is 24 m.

Answer: Given, l = 21m, r = 24/2 = 12 m
TSA (cone) = πr(l + r)
= (22/7) × 12 (21 + 12)
= 1244.57 m² (Answer)

CBSE Class 12 - English (Elective)- Sample Question Paper (2016-17) (#cbsepapers)

CBSE Class 12 - English (Elective)- Sample Question Paper (2016-17) 


☛See English (Elective) Marking Scheme of Sample Question Paper (2016-17)

CBSE Class 9 Maths - Surface Areas and Volumes - NCERT Exercise 13.2 (#cbseclass9Notes)

Surface Areas and Volumes

NCERT Exercise 13.2

Q1: The curved surface area of a right circular cylinder of height 14 cm is 88 cm². Find the diameter of the base of the cylinder.

Answer: Given, h = 14 cm,
curved, surface area (CSA) = 88 cm², r = ?
CSA  = 2πrh
⇒ 88 = 2 × (22/7) × r × 14
⇒ 88 = 44 × 2 × r
⇒ r = 88/88 = 1
∴ diameter = 2r = 2 cm


Q2: It is required to make a closed cylindrical tank of height 1 m and base diameter 140 cm from a metal sheet. How many square metres of the sheet are required for the same?.

CBSE Class 10 - संस्कृत (Sanskrit Communicative) SA2 Sample Question Paper (2016-17)

CBSE Class 10 - संस्कृत  (Sanskrit Communicative) Sample Question Paper (2016-17) 

CBSE Class 9 Maths - SURFACE AREAS AND VOLUMES (NCERT EXERCISE 13.1) (#cbsenotes) (#ncertsolutions)

SURFACE AREAS AND VOLUMES

Class 9 Maths 

NCERT EXERCISE 13.1

Q1: A plastic box 1.5 m long, 1.25 m wide and 65 cm deep is to be made. It is to be open at the top. Ignoring the thickness of the plastic sheet, determine :
(i) The area of the sheet required for making the box.
(ii) The cost of sheet for it, if a sheet measuring 1 m2 costs Rs 20.

Answer: Given,
l = 1.5 m,
b = 1.25 m,
h = 65 cm = 0.65 m

(i) ∵ the box is open at the top, it has only five faces.

Surface Area (SA) for five faces = lb + 2(bh + hl)

= 1.5 × 1.25 m² + 2 (1.25 × 0.65 + 0.65 × 1.5) m²
= 1.875 + 2 (1.7875) m² = 1.875 + 3.575
= 5.45 m²

(ii) Cost of 1 m² of the sheet = ₹ 20
∴ cost of 5.45 m² of the sheet = 20 × 5.45 m² = ₹ 109 (Answer)


Q2: The length, breadth and height of a room are 5m, 4m and 3m respectively. Find the cost of white washing the walls of the room and the ceiling at the rate of Rs 7.50 per m².