Question 1
2 marksThe plan of a solid is a square of side 5 cm.
The front elevation of the same solid is also a square of side 5 cm.
Owen says, "The solid must be a cube."
Is Owen correct?
Give a reason for your answer.
Model answer
No, Owen is not correct.
For example, a cylinder with diameter 5 cm and length 5 cm, lying on its curved surface with its length going from left to right, has a square plan (5 cm by 5 cm) and a square front elevation (5 cm by 5 cm), but its side elevation is a circle.
So the solid does not have to be a cube; you need the side elevation as well.
Explanation
Two views do not always fix a solid. Think of other solids that look like a 5 cm square from the front and from above. A cylinder lying on its side or a triangular prism can both do this, which is why plans and elevations are usually given as a set of three views.
Mark scheme
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1 mark
C1 for No (not necessarily)
must be supported by a reason to score
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1 mark
C1 for a correct counter-example, e.g. a cylinder of diameter 5 cm and length 5 cm lying on its curved surface with its axis from left to right (its side elevation is a circle), or a triangular prism 5 cm long whose side elevation is a triangle of base 5 cm and height 5 cm
any valid solid that is not a cube