Video: KS1-M16 • Paper 2 • Question 17

KS1-M16-P2-Q17-309171682406

04:33

Video Transcript

Which shape has exactly five faces? Write the letter.

This could be a tricky question to answer, and we’ll go through why in a moment. But let’s have a look at the five shapes that we have to look at. They’re all 3D or solid shapes. Shape A is a sphere, like a ball. Shape B, or recognised from eating ice creams, it’s a cone. Shape C is a cylinder. Shape D we call a triangular prism. And shape E is a cube. We don’t need to use these names in our answer. We’re just told to write the letter. But it’s always good to remind ourselves what the names of the shapes are.

We’re asked which shape has exactly five faces. A face on a shape is a flat surface. Some shapes have curved surfaces as well. But the face is a flat surface. So the question is asking us which of these shapes has five flat surfaces. And this is why the question’s tricky. We’re looking at pictures of solid shapes.

The best way to answer the question will be to pick the shape up and have a really good look all the way around it. But we can’t do that. We’re just looking at pictures of 3D shapes. So we have to try and think about what the shape looks like in our mind and imagine turning it and imagine what all the different parts of the shape are like. We call this visualising the shape. It means picturing it in our minds.

So let’s go through each shape and picture what it looks like and find the one that has exactly five faces. First, shape A, the sphere. We know that a sphere or a ball shape isn’t flat at all. That’s why it rolls. If we turn this sphere, it’s curved all the way around. It has one curved surface. So we know a sphere has no faces. A is not the answer we’re looking for.

Let’s look at shape B, the cone. The cone does have a face. This is the circle on the end. If we turned it upside down, it would be able to stand on the table. But we can also see that it has a curved surface that goes all the way around. Shape B is not the answer.

On to shape C, the cylinder, like a tin of beans. A cylinder has two faces. We can see one of them on the top. It’s a circle. But the other one is hidden. And this is why we need to be able to picture the shapes in our mind. Imagine picking this shape up and turning it upside down. We’d be able to see that there’s another circular face on the bottom. A cylinder also has a curved surface. If we turned our tin of beans on its side, it would roll down the hill. So with only two faces, we know that shape C is not correct.

Shapes D and E are a little more tricky than the others because more faces are hidden. Shape D has a triangle at the other end that we can’t see. So that’s two triangular faces. And then it has three rectangular faces around the shape. There’s this grey one that we can see. There’s the base that’s underneath that we can’t see. And if we imagine turning the shape, there’d be another rectangular face on the left-hand side too. Two triangular faces, three rectangular faces makes five faces all together. Looks Like D is our answer.

Let’s just check that a cube doesn’t have five faces. A cube has square faces all the way around. Let’s count them. There’s one on the front. And then opposite to that, there’s a square on the very back of the shape that we can’t see. So that’s two faces. Then there’s a grey one on the right that we can see. And if we can visualise turning the shape, there’d also be one opposite to that on the left-hand side. So that’s four faces we found. Then there’s one on the top and one on the bottom. Six faces on a cube.

We found the answer by picturing or visualising each shape in our mind and imagining turning it. The shape that has exactly five faces is the triangular prism, which is shape D.

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