Volume and Surface Area of Solid Figures


  1. The diameter of the Moon is approximately one-fourth of the diameter of the Earth. What is the ratio (approximate) of their volumes ?









  1. View Hint View Answer Discuss in Forum

    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


  1. A sphere and a hemisphere have the same surface area. The ratio of their volumes is ?









  1. View Hint View Answer Discuss in Forum

    According to the question,
    Surface area of sphere = Surface area of hemisphere
    4πr12 =3πr22
    ⇒ r1/r2 = √3/2

    Correct 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



  1. Find the number of lead balls of diameter 2 cm each, that can be made from a sphere of diameter 16 cm. ?









  1. View Hint View Answer Discuss in Forum

    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

    Correct 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


  1. 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. ?









  1. View Hint View Answer Discuss in Forum

    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

    Correct 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



  1. If the surface area of a sphere is 616 sq cm, what is its volume ?









  1. View Hint View Answer Discuss in Forum

    Curved surface area of the sphere = 4πr2
    Volume of the sphere = (4/3)πr3

    Correct 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