Page 273 - Start Up Mathematics_7

Can we have a cut which is neither vertical
nor horizontal? Yes, we can have an oblique
(slant) cut as shown. What is the cross-
section in this case? The boundary of the cross-section is a plane curve. Can you guess? Yes, its

a rectangle.

A kitchen play
Have you been to a kitchen when the vegetables are being cut. One can notice different
cross-sections of vegetables like radish, turnip, carrot, etc. Observe how different shapes are
obtained by making slices at different angles.

Example 4: Determine the cross-section made in the following solids by making a:
(a) vertical cut (b) horizontal cut
(i) Cuboid (ii) Cube (iii) Cylinder

(iv) Cone (v) Sphere (vi) Right triangular prism
Also draw rough sketch of the solids and verify using clay models.

Solution: Name of solid Sketch Vertical cut Horizontal cut

(i) Cuboid Square or rectangle Rectangle

(ii) Cube Square Square

(iii) Cylinder Rectangle Circle

(iv) Cone Triangle Circle

(v) Sphere Circle Circle

Right triangular
(vi) Rectangle A right triangle
prism

Shadow play
With the help of shadows, a 3-D object can be viewed in 2-D. All you need is a source of light
and a few solid shapes. One can use an overhead projector as a source of light if its available in
your school. If not, a torch can serve the purpose.

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