9. Conversion of Solids
Important Principle: Volume remains constant when solid is melted and recast into different shape.
If solid A is melted to form solid B:
Volume of A = Volume of B
Number of smaller solids = Volume of bigger solid ÷ Volume of smaller solid
11. Example Problems (NCERT Style)
Problem 1: A cone of height 24 cm and radius 6 cm is made. Find its volume and curved surface area.
Solution:
Volume = (1/3)pr²h = (1/3) × (22/7) × 6² × 24
= (1/3) × (22/7) × 36 × 24 = (22 × 36 × 8)/7 = 6336/7 ˜ 905.14 cm³
Slant height l = v(h² + r²) = v(576 + 36) = v612 = 6v17 cm
CSA = prl = (22/7) × 6 × 6v17 ˜ 132v17/7 cm²
Problem 2: A hemispherical bowl of internal diameter 36 cm contains liquid. This liquid is to be filled into cylindrical bottles of radius 3 cm and height 6 cm. How many bottles are needed?
Solution:
Radius of hemisphere = 18 cm
Volume of hemisphere = (2/3)pr³ = (2/3) × p × 18³ = 3888p cm³
Volume of one bottle = pr²h = p × 3² × 6 = 54p cm³
Number of bottles = 3888p ÷ 54p = 72 bottles
Problem 3: A cuboidal water tank is 6 m long, 5 m wide and 4.5 m deep. How many liters of water can it hold?
Solution:
Volume = l × b × h = 6 × 5 × 4.5 = 135 m³
1 m³ = 1000 liters
Capacity = 135 × 1000 = 135,000 liters