Question

a hollow cylindrical pipe is 21 cm long. Its inner and outer diameters are 6cm and 10 cm ,respectively.Find the volume of the metal used in making the pipe.

Answer 1

volume of cylinder = π(R²-r²)*h
                               = π(5²-3²)*21
                               = π(25-9)*21
                               = π(16)*21
                               = 22÷7×16×21
                               = 1056 cm³

Answer 2

The volume of the used metal 1056 cm³

Given data :

Outer diameter = 10 cm

Inner diameter = 6 cm

Height = 21 cm

So,the outer radius = 10/2 = 5 cm

Inner radius = 6/2 = 3 cm

So, hollow space volume = π ×(3)²×21 = 22/7×9×21 = 594 cm³

So, total volume = π × (5)² × 21 = 22/7 × 25 × 21 = 1650 cm³

Metal volume = (1650-594) = 1056 cm³