Question

a metallic hollow cylinder is 21 m deep. its outer and inner diameters are 21m deep and 14m respectively. find the cost of polishing the inner curved surface and outer curved surface at the rate of RS 25 per m².​

Answer 1

Answer:

★ Cost of polishing = Rs 57,750 ★

Step-by-step explanation:

Given:

• Depth of hollow cylinder is 21 m
• Outer and inner diameters are 21m & 14m respectively.
• Cost of polishing is Rs 25/m²

To Find:

• Total cost of polishing inner CSA and outer CSA of cylinder

Solution: We know that Radius = D/2

∴ Outer radius= D/2 = 21/2 = 10.5 m(r¹)

∴ Inner radius = D/2 = 14/2 = 7 m(r²)

★ Curved Surface area of Cylinder=2πrh

Therefore, Total CSA = 2πr¹h + 2π²h

$\small\implies{\sf }$ Total CSA = 2πh ( r¹ + r² )

$\small\implies{\sf }$ Total CSA = 2 x 22/7 x 21 (10.5+7)

$\small\implies{\sf }$ Total CSA = 44 x 3 x 17.5

$\small\implies{\sf }$ Total CSA = 2310 m²

• Cost of polishing 1m² = Rs 25

∴ Cost of polishing 2310m² = 2310 x 25= Rs 57,750

Answer 2

Answer:

★ Cost of polishing = Rs 57,750 ★

Step-by-step explanation:

Given:

Depth of hollow cylinder is 21 m

Outer and inner diameters are 21m & 14m respectively.

Cost of polishing is Rs 25/m²

To Find:

Total cost of polishing inner CSA and outer CSA of cylinder

Solution: We know that Radius = D/2

∴ Outer radius= D/2 = 21/2 = 10.5 m(r¹)

∴ Inner radius = D/2 = 14/2 = 7 m(r²)

★ Curved Surface area of Cylinder=2πrh

Therefore, Total CSA = 2πr¹h + 2π²h

Total CSA = 2πh ( r¹ + r² )

Total CSA = 2 x 22/7 x 21 (10.5+7)

Total CSA = 44 x 3 x 17.5

Total CSA = 2310 m²

• Cost of polishing 1m² = Rs 25

∴ Cost of polishing 2310m² = 2310 x 25= Rs 57,750