Volume and Surface Area of Solid Figures


  1. The volumes of a sphere and a right circular cylinder having the same radius are equal. The ratio of the diameter of the sphere to the height of the cylinder is ?









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    Let r = Radius of cylinder = Radius of sphere, h = Height of the cylinder.
    According to the question.
    4/3πr3 = πr2h

    Correct Option: D

    Let r = Radius of cylinder = Radius of sphere, h = Height of the cylinder.
    According to the question.
    4/3πr3 = πr2h
    ⇒ h = 4r/3
    ⇒ 4r = 3h
    ⇒ 2r = 3/2h
    ⇒ 2r/h = 3/2
    ∴ Required ration = 3 : 2


  1. How many spherical bullets can be made out of a solid cube whose edge measures 44 cm, each bullet being 4 cm in diameter ?









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    Volume of 1 bullet = 4/3π(2)3 = (32/3 x 22/7) cm3
    Volume of the cube = (44)3

    Correct Option: B

    Volume of 1 bullet = 4/3π(2)3 = (32/3 x 22/7) cm3
    Volume of the cube = (44)3
    ∴ Number of bullets = Volume of solid/Volume of 1 bullet
    = (44)3 x 3 x 7 / 32 x 22 = 2541



  1. A hemisphere has 28 cm diameter. Find its curved surface area. ?









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    Curved surface area = 2πr2

    Correct Option: A

    Curved surface area = 2πr2
    = 2π x 14 x 14 = 2 x (22/7) x 14 x 14
    = 2 x 22 x 2 x 14
    = 88 x 14
    = 1232 sq cm


  1. If the ratio of the diameters of two spheres is 3: 5, then what is the ratio of their surface areas ?









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    Let the diameter's of two sphere are d1 and d2, respectively.
    ∴ Ratio of their surface areas = 4πr12/4πr22

    Correct Option: A

    Let the diameter's of two sphere are d1 and d2, respectively.
    ∴ Ratio of their surface areas = 4πr12/4πr22
    = (2r1)2/(2r2)2 = d12/d22
    = (d1/d2)2 = (3/5)2 = 9/25 = 9 : 25



  1. If 64 identical small spheres are made out of a big sphere of diameter 8 cm, what is surface area of each small sphere ?









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    Volume of small spheres
    = Volume of bigger sphere / Number of small spheres = [(4/3)π(4)3] / 64
    = [(4/3) x π x 4 x 4 x 4] / 64
    = 4/3 π cm3

    Let radius of small sphere be r
    ∴ 4/3πr3 = 4π/3
    ⇒ r2 = 1 cm

    Correct Option: C

    Volume of small spheres
    = Volume of bigger sphere / Number of small spheres = [(4/3)π(4)3] / 64
    = [(4/3) x π x 4 x 4 x 4] / 64
    = 4/3 π cm3

    Let radius of small sphere be r
    ∴ 4/3πr3 = 4π/3
    ⇒ r2 = 1 cm
    Now, surface area of small sphere = 4πr2 = 4π cm2