Volume and Surface Area of Solid Figures


  1. The volume of a right circular cone is 100π cm3 and its height is 12 cm. Find its slant height. ?









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    Volume = (1/3)πr2h
    According to the question,
    (1/3)πr2h = 100π
    ⇒ (1/3)πr2 x 12 = 100π
    ⇒ r2 = 25
    ∴ r = √25 = 5 cm
    ∴ Slant height (l) = √h2 + r2

    Correct Option: A

    Volume = (1/3)πr2h
    According to the question,
    (1/3)πr2h = 100π
    ⇒ (1/3)πr2 x 12 = 100π
    ⇒ r2 = 25
    ∴ r = √25 = 5 cm
    ∴ Slant height (l) = √h2 + r2
    = √122 + 52
    = √169 = 13 cm


  1. What is volume of a cone having a base of radius 10 cm and height 21 cm ?









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    Volume of cone = (1/3)πr2h
    = (1/3) x (22/7) x 10 x 10 x 21

    Correct Option: A

    Volume of cone = (1/3)πr2h
    = (1/3) x (22/7) x 10 x 10 x 21 = 2200 cm3



  1. The diameter of the base of a cone is 6 cm and altitude is 4 cm, What is the approximate curved surface area of the cone ?









  1. View Hint View Answer Discuss in Forum

    Radius of cone (r) = 6/2 = 3 cm
    and height of cone (h) = 4cm
    Slant height (l) = √h2 + r2
    = √(4)2 + (3)2
    = √16 + 9
    = 5 cm
    Now, curved surface area = πrl

    Correct Option: B

    Radius of cone (r) = 6/2 = 3 cm
    and height of cone (h) = 4cm
    Slant height (l) = √h2 + r2
    = √(4)2 + (3)2
    = √16 + 9
    = 5 cm
    Now, curved surface area = πrl
    = (22/7) x 3 x 5
    = 330/7 = 47 cm2


  1. The diameter if base of a right circular cone is 7 cm and height is 10 cm , then what is its lateral surface area ?









  1. View Hint View Answer Discuss in Forum

    Given that,
    Diameter of a right circular cone = 7 cm
    ∴ Radius of a right circular cone = 7/2 cm
    and slant height of a right circular cone (l) = 10 cm
    ∴ Lateral surface area of a cone = πrl = (22/7) x (7/2) x 10

    Correct Option: A

    Given that,
    Diameter of a right circular cone = 7 cm
    ∴ Radius of a right circular cone = 7/2 cm
    and slant height of a right circular cone (l) = 10 cm
    ∴ Lateral surface area of a cone = πrl = (22/7) x (7/2) x 10
    = 11 x 10 = 110 cm2



  1. If the volume of a right circular cone of height 9 cm is 48π cm3, then find the diameter of its base. ?









  1. View Hint View Answer Discuss in Forum

    volume = 48 π cm3 and h = 9 cm
    ∴ (1/3)πr2h = 48π
    ⇒ (1/3) x π x r2 x 9 = 48π

    Correct Option: A

    volume = 48 π cm3 and h = 9 cm
    ∴ (1/3)πr2h = 48π
    ⇒ (1/3) x π x r2 x 9 = 48π
    ∴ r2 = (48π x 3) / (π x 9) = 16
    ∴ r = √16 = 4 cm
    ∴ Diameter = 2r = 2 x 4 = 8 cm