Question

An iron pillar has some part in the form of a right circular cylinder and remaining in the form of a right circular cone. The radius of the base of each of cone and cylinder is 8 cm. The cylinderical part is 240 cm high and the conical part in 36 cm high. Find the weight of the pillar if one cu. cm of iron weighs 7.8 grams.​

Answer 1

GIVEN

• Radius = 8 cm

• Height of cylinder = 240 cm

• the conical part in 36 cm high..

TO FIND

Weight of the pillar if one cu. cm of iron weighs 7.8 grams.

SOLUTION ✍

We know that

Volume of cylinder = πr²h

Volume of cone = ⅓πr²h

Volume of cylinder

= 3.14 × 8 × 8 × 240

= 48320.4 cm³

Volume of cone

= ⅓ × 3.14 × 8 × 8 × 36

= 1 × 3.14 × 8 × 8 × 12

= 3.14 × 64 ×12

= 2411.52 cm³

Now,

Weight of pillar = Volume of cylinder + volume of cone

W = 48320.4 + 2411.52

W = 50730

1kg = 1000gm

7.8/1000 × 50730

0.0078 × 50730

395.4 kg

Weight of pillar is 395 kg

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Answer 2

GIVEN

• Radius = 8 cm
• Height of cylinder = 240 cm
• The conical part = 36 cm high

TO FIND

• Weight of the pillar if one cu. cm of iron weighs 7.8 grams.

FORMULA USED

• Volume of cylinder = πr²h
• Volume of cone = ⅓πr²h

SOLUTION

Volume of cylinder

= 3.14 × 8 × 8 × 240

= 48320.4 cm³

Volume of cone

= ⅓ × 3.14 × 8 × 8 × 36

= 1 × 3.14 × 8 × 8 × 12

= 3.14 × 64 ×12

= 2411.52 cm³

Now,

Weight of pillar = Volume of cylinder + volume of cone

W = 48320.4 + 2411.52

W = 50730

• 1kg = 1000gm

7.8/1000 × 50730

0.0078 × 50730

395.4 kg

★ Weight of pillar is 395 kg

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