Volume and Surface Area of Solid Figures
- The diameter of the Moon is approximately one-fourth of the diameter of the Earth. What is the ratio (approximate) of their volumes ?
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Given that, the diameter of moon is approximately one-fourth of the diameter of Earth.
Let radius on moon = r
Then, radius of Earth = 4r
∴ Volume of Moon/Volume of Earth
= [(4/3)πr3] / [(4/3)π(4r)3]Correct Option: B
Given that, the diameter of moon is approximately one-fourth of the diameter of Earth.
Let radius on moon = r
Then, radius of Earth = 4r
∴ Volume of Moon/Volume of Earth
= [(4/3)πr3] / [(4/3)π(4r)3]
= [r3] / [64r3] = 1/64 = 1 : 64
- A sphere and a hemisphere have the same surface area. The ratio of their volumes is ?
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According to the question,
Surface area of sphere = Surface area of hemisphere
4πr12 =3πr22
⇒ r1/r2 = √3/2Correct Option: D
According to the question,
Surface area of sphere = Surface area of hemisphere
4πr12 =3πr22
⇒ r1/r2 = √3/2
∴ Ratio in volume = [(4/3)πr13] / [(4/3)πr23]
= 3√3/8 : 1
- Find the number of lead balls of diameter 2 cm each, that can be made from a sphere of diameter 16 cm. ?
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Radius of the sphere = 16/2 = 8 cm
Volume of the sphere = (4/3) x π x 8 x 8 x 8 cm3
Radius of each lead ball = 2/2 = 1 cm
Volume of each lead ball = Volume of sphere / Volume of lead ballCorrect Option: D
Radius of the sphere = 16/2 = 8 cm
Volume of the sphere = (4/3) x π x 8 x 8 x 8 cm3
Radius of each lead ball = 2/2 = 1 cm
Volume of each lead ball = Volume of sphere / Volume of lead ball
= (4/3) π x 1 x 1 x 1 = 4π/3 cm3
∴ Number of lead balls = [(4/3) x π x 8 x 8 x 8 x 3] / [4 π]
= 8 x 8 x 8 = 512
- A hemispherical bowl has 3.5 cm radius. It is to be painted inside as well as outside. Find the cost of painting it at the rate of ₹ 5 per 10 sq cm. ?
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Curved surface area of the hemisphere = 2πr2
= 2 x (22/7) x (7/2) x (7/2) = 77 sq
As bowl is to painted inside and outside.
∴ Total surface to be painted = 77 x 2 = 154 sq cm
∴ Cost of painting 154 sq cm = (5/10) x 154Correct Option: D
Curved surface area of the hemisphere = 2πr2
= 2 x (22/7) x (7/2) x (7/2) = 77 sq
As bowl is to painted inside and outside.
∴ Total surface to be painted = 77 x 2 = 154 sq cm
∴ Cost of painting 154 sq cm = (5/10) x 154 = 1/2 x 154 = ₹ 77
- If the surface area of a sphere is 616 sq cm, what is its volume ?
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Curved surface area of the sphere = 4πr2
Volume of the sphere = (4/3)πr3Correct Option: A
Curved surface area of the sphere = 4πr2
or 616 = 4πr2
⇒ πr2 = 616/4 = 154
⇒ r2 = (154 x 7) / 22 = 49
∴ r = √49 = 7 cm
∴ Volume of the sphere = (4/3)πr3
= (4/3) x (22/7) x 7 x 7 x 7
= 4312 / 3 cm3