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Spheres and Cones

discia.org 10 questions · 33 marks
Name Date
  1. Either paper 2 marks

    An empty cylindrical container has radius \(8\) cm and height \(71\) cm. \(6\) identical balls are stacked directly on top of one another inside it. Each ball is a sphere of radius \(8\) cm.

    Will all \(6\) balls fit inside the container? Show working to support your answer.

    Show answer
    No — the 6 balls need a stacked height of \(96\) cm and the container is \(71\) cm tall.
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  2. Either paper 2 marks

    Here is a solid sphere of radius \(5\) cm.

    5 cm

    Surface area of a sphere \(= 4\pi r^2\)

    Find the surface area of the sphere. Give your answer in terms of \(\pi\).

    Show answer
    \(100\pi\ \text{cm}^2\)
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  3. Either paper 2 marks

    The diagram shows a solid sphere. It has a radius of \(15\) cm, so its diameter is \(30\) cm.

    15 cm

    The sphere is cut exactly in half, making a solid hemisphere.

    Volume of a sphere \(= \frac{4}{3}\pi r^3\)

    Marcus works out the volume of the hemisphere, in terms of \(\pi\). Here is his working:

    Volume of hemisphere \(= \frac{2}{3} \times \pi \times 30^{2} = 600\pi\) cm³

    Marcus has made two mistakes in this working.

    Write down the two mistakes he has made.

    Show answer
    Mistake 1: used the diameter in place of the radius. Mistake 2: squared instead of cubing (used power 2, not power 3). (Either order.)
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  4. Calculator 3 marks

    The diagram shows a solid sphere. The diameter of the sphere is \(20\) cm.

    20 cm

    Volume of a sphere \(= \frac{4}{3}\pi r^3\)

    Work out the volume of the sphere. Give your answer correct to 1 decimal place.

    Show answer
    \(4188.8\ \text{cm}^3\)
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  5. Either paper 5 marks

    A solid rubber ball is a sphere of radius \(12\) cm.

    12 cm

    The ball is cut exactly in half through its centre, making two identical solid hemispheres.

    Volume of a sphere \(= \frac{4}{3}\pi r^3\)

    Surface area of a sphere \(= 4\pi r^2\)

    (a)

    Calculate the volume of one of the hemispheres. Give your answer in terms of \(\pi\).

    (b)

    Calculate the total surface area of one of the hemispheres. Give your answer in terms of \(\pi\).

    Show answer
    (a) \(1152\pi\ \text{cm}^3\)
    (b) \(432\pi\ \text{cm}^2\)
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  6. Either paper 4 marks

    The diagram shows a cube with edges of length \(x\) cm, and a sphere of radius \(3\) cm.

    x cm 3 cm

    Surface area of a sphere \(= 4\pi r^2\)

    The surface area of the cube is equal to the surface area of the sphere.

    Show that \(x = \sqrt{ 6\pi }\).

    Show answer
    \(6x^2 = 36\pi\), so \(x^2 = 6\pi\) and \(x = \sqrt{ 6\pi }\).
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  7. Calculator 4 marks

    The diagram shows a sphere-shaped exercise ball. The ball has a radius of \(22\) cm.

    22 cm

    The ball already contains \(15.6\) litres of air. An electric pump then adds more air to the ball at a constant rate of \(1.5\) litres per minute.

    Volume of a sphere \(= \frac{4}{3}\pi r^3\)

    \(1\) litre \(= 1000\ \text{cm}^3\)

    Does it take less than \(15\) minutes to fill the ball completely? You must show your working.

    Show answer
    No — it takes \(19.3\) minutes to fill, which is more than the 15 minute threshold.
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  8. Calculator 4 marks

    A bowl is a hemisphere with radius \(10\) cm. The diagram shows the full sphere it is exactly half of, cut through its centre.

    10 cm

    Volume of a sphere \(= \frac{4}{3}\pi r^3\)

    Water is poured into the bowl at a rate of \(46.4\) cm³ per second for \(18\) seconds.

    Does the water fill more than \(45\%\) of the bowl? You must show your working.

    Show answer
    No — the water fills \(39.9\%\) of the bowl, and the question asks about \(45\%\).
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  9. Either paper 3 marks

    Two solid cones are shown before they are joined. Both cones have base radius \(r\) cm. One has slant height \(3r\) cm and the other has slant height \(4r\) cm.

    r cm3r cm r cm4r cm

    The two cones are then joined base to base to make one solid.

    Curved surface area of a cone \(= \pi r l\), where \(l\) is the slant height.

    The total surface area of the solid is \(323.68\pi\) cm².

    Calculate the radius \(r\).

    Show answer
    \(6.8\ \text{cm}\)
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  10. Either paper 4 marks

    A container in the shape of a sphere has radius \(8\) cm. A second container is a cone. The diagram shows the shape of the cone, which is used with its point downwards. The cone has base radius \(8\) cm and perpendicular height \(29\) cm. Both containers are to be filled with water. The diagrams are not drawn to scale.

    8 cm 29 cm8 cm

    Volume of a sphere \(= \frac{4}{3}\pi r^3\)

    Volume of a cone \(= \frac{1}{3}\pi r^2 h\)

    Which container holds more? You must show your working.

    Show answer
    The sphere holds more: the sphere is \(682\frac{2}{3}\pi\) cm³ and the cone is \(618\frac{2}{3}\pi\) cm³.
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discia.org Spheres and Cones · sheet 1
Answers Spheres and Cones · sheet 1
  1. No — the 6 balls need a stacked height of \(96\) cm and the container is \(71\) cm tall.
  2. \(100\pi\ \text{cm}^2\)
  3. Mistake 1: used the diameter in place of the radius. Mistake 2: squared instead of cubing (used power 2, not power 3). (Either order.)
  4. \(4188.8\ \text{cm}^3\)
  5. (a) \(1152\pi\ \text{cm}^3\)
    (b) \(432\pi\ \text{cm}^2\)
  6. \(6x^2 = 36\pi\), so \(x^2 = 6\pi\) and \(x = \sqrt{ 6\pi }\).
  7. No — it takes \(19.3\) minutes to fill, which is more than the 15 minute threshold.
  8. No — the water fills \(39.9\%\) of the bowl, and the question asks about \(45\%\).
  9. \(6.8\ \text{cm}\)
  10. The sphere holds more: the sphere is \(682\frac{2}{3}\pi\) cm³ and the cone is \(618\frac{2}{3}\pi\) cm³.
discia.org Spheres and Cones · sheet 1