Question

5. A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of
tin-plating it on the inside at the rate of 16 per 100 cm?.
Find the radius of a sphere whose surface area is 154 cm2​

Answer 1

Answer:

Q.1 ) A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of  tin-plating it on the inside at the rate of 16 per 100 cm?

A.1) Here, we will tin-plate inside of the hemisphere

So, we need to find the Curved Surface Area of hemisphere

Radius of sphere = r = diameter / 2 = 10.5  / 2 = 5.25 cm

Curved Surface Area of hemisphere = 2πr²

Curved Surface Area of hemisphere = { 2 x 22/7 x 5.25 x 5.25 } cm²

Curved Surface Area of hemisphere = 173.25 cm²

Cost of tin-plating 100 cm² = ₹16

Cost of tin-plating 1 cm² = ₹1/100 x 16

Cost of tin-plating 173.25 cm² = ₹1/100 x 16 x 173.25

Cost of tin-plating 173.25 cm² = ₹27.72

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Q.2) Find the radius of a sphere whose surface area is 154 cm² ?

A.2) Let r be the radius of sphere

Surface Area of Sphere = 4πr²

154 = 4πr²

154 = 4 x 22/7 x r²

154 x 7 / 22 x 4 = r²

r² = 12.25

r = √12.25

r = 3.5 cm