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VOLUME AND SURFACE AREA

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VOLUME AND SURFACE AREA -> IMPORTANT FACTS AND FORMULAE

I. CUBIOD
Let length = l, breadth = b and height = h units. Then,
1. Volume = (l x b x h) cubic units.
2. Surface area = 2 (lb + bh + lh)
II. CUBE
Let each edge of a cube be of length a. Then, 1. Volume = a³ cubic units.
2. Surface area = 6a² sq. units.
3. Diagonal = √3 a units.
III. CYLINDER
Let radius of base = r and Height (or length) = h Then,
1. Volume = (∏r²h) cubic units.
2. Curved surface area = (2∏rh) sq. units.
3. Total surface area = (2∏rh + 2∏r² sq. units)
= 2∏r (h + r) sq. units.
IV. CONE
Let radius of base = r and Height = h. Then,
1. Slant height, l = √h² + r ² units.
2. Volume = [1/3 ∏r²h] cubic units.
3. Total surface area = (∏rl + ∏r²) sq.units.
V. SPHERE
Let the radius of the sphere be r. Then,
1. Volume = [4/3 ∏r3] cubic units.
2. Surface area = (4∏r²) sq. units.
VI. HEMISPHERE
Let the radius of a hemisphere be r. Then,
1. Volume = [2/3 ∏r3] cubic units.
2. Curved surface area = (3∏r²) sq. units.
3. Total surface area = (3∏r²) sq. units.
Remember : 1 litre = 1000 cm³.

VOLUME AND SURFACE AREA -> SOLVED EXAMPLES

1. The diagonal of a cube is 6√3 cm. Find its volume and surface area.
  Sol. Let the edge of the cube be a.
∴ √3a = 6 √3a = 6.
So, Volume = a³ = (6 * 6 * 6) cm³ = 216 cn³
Surface area = 6a² = (6 * 6 * 6) cm² = 216 cm²
2. Find the volume and surface area of a cuboid 16m long, 14m broad and 7m high.
  Sol. Volume = (16 * 14 * 7) m³ = 1568 m³
Surface area = [2 (16 * 14 + 14 * 7 + 16 * 7)] cm² = (2 * 434) cm²
= 868 cm².
3. If the capacity of a cylindrical tank is 1848 m³ and the diameter of its base is 14m, then find the depth of the tank.
  Sol.Let the depth of the tank be h metres. then,
∏ * (7)² * h = 1848 ⇔ h = [1848 * 7/22 * 1/7*7] = 12 m.
4. How many iron rods, each of length 7m and diameter 2cm can be made out of 0.88 cubic metre of iron?
  Sol. Volume of 1 rod = [22/7 * 1/100 * 1/100 * 7] cu. m = 11/5000 cu.m.
Volume of iron = 0.88 cu. m.
Number of rods = [0.88 * 5000/11] = 400.
5. A cube of edge 15 cm is imersed completely in a rectangular vessel containing water. If the dimensions of the base of vessel are 20 cm * 15 cm, find the rise in waer level.
  Sol. Increase in volume = Volume of the cube = (15 * 15 * 15) cm³.
∴ Rise in water level = [Volume/Area] = [15 * 15 * 15/20 * 15] cm = 11.25 cm.
6. How many spherical bullets can be made out of a lead cylinder 28 cm high and with base radius 6 cm, each bullet being 1.5 cm ub duaneter?
  Sol. Volume of cylinder = (∏ * 6 * 6 * 28) cm³ = (36 * 28) ∏ cm³.
Bolume of each bullet = [4/3 ∏ * 3/4 * 3/4 * 3/4] cm³ = 9∏/16 cm³.
Number of bullets = Volume of cylinder / Volume of each bullet
= [(36 * 28)∏ * 16/9∏] = 1792.

VOLUME AND SURFACE AREA -> EXERCISE

1. Three cubes of iron whose edges are 6cm, 8cm and 10cm respectively are melted and formed into a single cube. The edge of the new cube formed is
 
  • A. 10 cm
  • B. 12 cm
  • C. 16 cm
  • D. 18 cm
Ans: B.
Sol.
Volume of the new cube
= (63 + 83 + 103) cm3
= 1728cm3.
Let the edge of the new cube be a cm.
∴ a3 = 1728
⇒ a = 12.
 
2. A metallic sheet is of rectangular shape with dimensions 48 m x 36 m. From each of its corner, a square is cut off so as to make an open box. If the length of the square is 8 m, the volume of the box (in m3) is
 
  • A. 6420
  • B. 8960
  • C. 5120
  • D. 4830
Ans: C.
Sol.
Clearly, l = (48 - 16) m = 32 m,
b = (36 - 16) m = 20 m,
h= 8 m.
∴ Volume of the box = (32 x 20 x 8) m3 = 5120 m3
 
 
3. A rectangular box measures internally 1.6 m long, 1 m broad and 60 cm deep. The number of cubical blocks each of edge 20 cm that can be packed inside the box is
 
  • A. 30
  • B. 60
  • C. 120
  • D. 150
Ans: C.
Sol. Number of blocks =
160x100x60
20x20x20] = 120.