Question

An electric lamp is in the shape of a glass hemispherical base surmounted by a metallic cylindrical top of radius 21 cm and height 3.5 cm . The top was silver coated and the glass surface was painted red.

1) What is the cost of silver coating the top at the rate of Rs 5 per
100cm²?
2) What is the surface area of glass to be painted red ?

Answer 1

||✪✪ QUESTION ✪✪||

An electric lamp is in the shape of a glass hemispherical base surmounted by a metallic cylindrical top of radius 21 cm and height 3.5 cm . The top was silver coated and the glass surface was painted red.

1) What is the cost of silver coating the top at the rate of Rs 5 per

100cm²?

2) What is the surface area of glass to be painted red ?

|| ★★ FORMULA USED ★★ ||

• CSA of Hemisphere = 2πr²
• CSA of cylinder = 2πrh

|| ✰✰ ANSWER ✰✰ ||

Since, it is given that, glass hemispherical base was painted Red ,, and its on top of cylinder, so its radius will be same as radius of cylinder ,

So,

CSA of Hemisphere = 2πr² .

→ CSA = 2 * (22/7) * (21) * (21)

→ CSA = 2 * 22 * 3 * 21

→ CSA = 2772 cm² .

Hence, The surface area of glass to be painted red is 2772cm².

________________________

Now,

→ CSA of cylinder = 2 * (22/7) * 21 * 3.5

→ CSA = 2 * 22 * 3 * 3.5

→ CSA = 462cm².

So, silver painted Area is 462cm².

now,

→ 100cm² silver painted cost = Rs.5

→ 1 cm² silver painted cost = (5/100)

→ 462cm² silver painted cost = (1/20) * 462 = Rs.23.1 .

Hence, cost of silver painted Area is Rs.23.1 ..

Answer 2

QUESTION :-

An electric lamp is in the shape of a glass hemispherical base surmounted by a metallic cylindrical top of radius 21 cm and height 3.5 cm . The top was silver coated and the glass surface was painted red.

1) What is the cost of silver coating the top at the rate of Rs 5 per

100cm²?

2) What is the surface area of glass to be painted red ?

FORMULA USED :-

CSA of Hemisphere is = 2πr²

and

CSA of cylinder = 2πrh

ANSWER :-

Radius of Hemisphere = Radius of Cylinder

=> CSA = 2 * (22/7) * (21) * (21)

=> CSA = 2 * 22 * 3 * 21

=> CSA = 2772 cm² .

now, we have to Find CSA of cylinder ,,

=> CSA of cylinder = 2 * (22/7) * 21 * 3.5

=> CSA = 2 * 22 * 3 * 3.5

=> CSA = 462cm².

So, silver painted Area is 462cm².

now, given that 100cm² silver painted cost is Rs.5.

=> 100cm² silver painted cost = Rs.5

=> 1 cm² silver painted cost = (5/100)

=> 462cm² silver painted cost = (1/20) * 462 = Rs.23.1 .

Hence, cost of silver painted Area is Rs.23.1 ..