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Spheres and Cones

discia.org 10 questions · 32 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 Higher1 mark

    A cup is in the shape of a cone. It is full of cola. The diagram shows the shape of the cup, which is used with its point downwards.

    15 cm

    The full depth of the cup is \(15\) cm. Ben drinks some of the cola, until the depth of cola left in the cup is \(10\) cm.

    Ben says, "The fraction of the cola still in the cup, by volume, is \(\frac{ 4 }{ 9 }\)."

    Is the fraction that Ben gives correct? Tick a box.

    Yes / No

    Give a reason for your answer.

    Show answer
    No — the depth is \(\frac{ 2 }{ 3 }\) of the full depth, so the volume left is \(\left(\frac{ 2 }{ 3 }\right)^3 = \frac{ 8 }{ 27 }\) of the cola.
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  3. Either paper 2 marks

    The diagram shows a solid sphere of radius \(10\) cm.

    10 cm

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

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

    Show answer
    \(400\pi\ \text{cm}^2\)
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  4. Either paper 2 marks

    Here is a solid sphere. It has a radius of \(12\) cm, so its diameter is \(24\) cm.

    12 cm

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

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

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

    Volume of hemisphere \(= \frac{4}{3} \times \pi \times 12^{2} = 192\pi\) cm³

    Amara has made two mistakes in this working.

    Write down the two mistakes she has made.

    Show answer
    Mistake 1: kept the full-sphere fraction, 4/3, instead of the hemisphere fraction, 2/3 (missed the ÷2 for a hemisphere). Mistake 2: squared instead of cubing (used power 2, not power 3). (Either order.)
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  5. Calculator 3 marks

    The diagram shows a solid sphere. The diameter of the sphere is \(18\) cm.

    18 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
    \(3053.6\ \text{cm}^3\)
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  6. Either paper 5 marks

    A solid wooden ball is a sphere of radius \(6\) cm.

    6 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)

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

    (b)

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

    Show answer
    (a) \(144\pi\ \text{cm}^3\)
    (b) \(108\pi\ \text{cm}^2\)
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  7. Either paper Higher5 marks

    Here is a solid cone. The radius of its base is \(8\) cm and its slant height is \(17\) cm.

    h cm8 cm17 cm

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

    (a)

    Work out the vertical height \(h\) of the cone.

    (b)

    Work out the volume of the cone. Give your answer in terms of \(\pi\).

    Show answer
    (a) \(15\ \text{cm}\)
    (b) \(320\pi\ \text{cm}^3\)
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  8. Either paper 4 marks

    The diagram shows a cube with edges of length \(x\) cm, and a sphere of radius \(9\) cm.

    x cm 9 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 \(x = \sqrt{ 54\pi }\).

    Show answer
    \(6x^2 = 324\pi\), so \(x^2 = 54\pi\) and \(x = \sqrt{ 54\pi }\).
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  9. Calculator 4 marks

    The diagram shows a sphere-shaped exercise ball. The ball has a radius of \(23\) cm.

    23 cm

    The ball already contains \(20.9\) litres of air. An electric pump then adds more air to the ball at a constant rate of \(2\) litres per minute.

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

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

    Does it take less than \(11\) minutes to fill the ball completely? You must show your working.

    Show answer
    No — it takes \(15.1\) minutes to fill, which is more than the 11 minute threshold.
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  10. Calculator 4 marks

    A bowl is a hemisphere with radius \(9\) cm. The diagram shows the full sphere it is exactly half of, cut through its centre.

    9 cm

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

    Water is poured into the bowl at a rate of \(39.2\) cm³ per second for \(23\) seconds.

    Does the water fill less than \(55\%\) of the bowl? You must show your working.

    Show answer
    No — the water fills \(59.1\%\) of the bowl, and the question asks about \(55\%\).
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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. No — the depth is \(\frac{ 2 }{ 3 }\) of the full depth, so the volume left is \(\left(\frac{ 2 }{ 3 }\right)^3 = \frac{ 8 }{ 27 }\) of the cola.
  3. \(400\pi\ \text{cm}^2\)
  4. Mistake 1: kept the full-sphere fraction, 4/3, instead of the hemisphere fraction, 2/3 (missed the ÷2 for a hemisphere). Mistake 2: squared instead of cubing (used power 2, not power 3). (Either order.)
  5. \(3053.6\ \text{cm}^3\)
  6. (a) \(144\pi\ \text{cm}^3\)
    (b) \(108\pi\ \text{cm}^2\)
  7. (a) \(15\ \text{cm}\)
    (b) \(320\pi\ \text{cm}^3\)
  8. \(6x^2 = 324\pi\), so \(x^2 = 54\pi\) and \(x = \sqrt{ 54\pi }\).
  9. No — it takes \(15.1\) minutes to fill, which is more than the 11 minute threshold.
  10. No — the water fills \(59.1\%\) of the bowl, and the question asks about \(55\%\).
discia.org Spheres and Cones · sheet 1