Starter quiz
- A __________ is the 3D shape made from a cone by making a cut parallel to its circular base and removing the resultant smaller cone.
- frustum ✓
- hemi-cone
- semi-cone
-
- The left-hand cone is split into a smaller cone and a frustum. Match each length labelled a - c to its value.
- a⇔16 cm ✓
- b⇔4 cm ✓
- c⇔21 cm ✓
- The diagram shows a side elevation of a frustum. Find the volume of the large cone that the frustum is cut from. Give your answer correct to 3 significant figures.
- 219 000 cm³
- 309 000 cm³
- 803 000 cm³ ✓
- 3 210 000 cm³
-
- The diagram shows a side elevation of a frustum. Find the volume of the frustum. Give your answer correct to 3 significant figures.
- 214 000 cm³
- 314 000 cm³
- 414 000 cm³
- 494 000 cm³ ✓
- 1 110 000 cm³
-
- A cone is cut into a frustum of height 20 cm and a small cone. The radius of the base of the frustum is 15 cm and the radius of its top is 12 cm. The height of the small cone is ______ cm.
- '80' ✓
- The diagram shows a large cone with a frustum of height 20 cm and a small cone. The radius of the frustum base is 15 cm and the radius of its top is 12 cm. The volume of the frustum is ______𝜋 cm³.
- '3660' ✓
Exit quiz
- A circular cone has ______ surfaces.
- '2' ✓
- The area of the curved surface of this frustum is ______𝜋 cm². Leave your answer in terms of 𝜋.
- '1080' ✓
- The total surface area of this frustum is ______𝜋 cm². Leave your answer in terms of 𝜋.
- '1692' ✓
- Work out the length of the side marked on this frustum.
- 8 cm
- 9 cm
- 10 cm ✓
- 11.31 cm
- 11.61 cm
-
- Find the area of the curved surface of this frustum. Leave your answer in terms of 𝜋.
- 110𝜋 cm²
- 115𝜋 cm²
- 120𝜋 cm² ✓
- 125𝜋 cm²
-
- The total surface area of this frustum is ______𝜋 cm². Leave your answer in terms of 𝜋.
- '210' ✓
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- The frustum of a cone can be thought of as a cone with the top missing.
- Calculating the surface area for the frustum of a cone is a similar method to finding the area.
- There is an extra face to consider, the top of the frustum.
Common misconception
Pupils may confuse the slant length (which is needed to find the curved surface area of the cone or frustum) with the perpendicular (or vertical) height.
Encourage pupils to clearly label their diagrams, indicating the perpendicular height with a right-angle symbol. They may need to use Pythagoras' theorem or trigonometry to calculate the slant length.
Keywords
Frustum - A frustum is the 3D shape made from a cone by making a cut parallel to its circular base and removing the resultant smaller cone.
Surface area - The surface area is the total area of all the surfaces of a closed 3D shape. The surfaces include all faces and any curved surfaces.
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