Question

The figure shows part of the concrete slab which is used to make drains and its cross-section. it is made up of a cuboid of dimensions 120 cm by 60 cm by 40 cm, with a half-cylinder horizontally carved out of it.
(i) find the area of the cross-section ABCDEFG.
(ii) find the volume of the concrete slab.
(iii) find the total surface area of the concrete slab.
(iv) find the mass of the concrete slab if the density of concrete is 2300 kg/cubic m, giving your answer in kg.

Answer 1

(i) The area of the cross section ABCDEFG is 1771.6cm³

(ii) The volume of the concrete lab is 212592 cm³

(iii) the total surface area of the concrete slab is 30284 cm²

(iv) The mass of the concrete slab is 40746.8 kg/m³.

Given, dimensions are 120 cm by 60 cm by

40 cm.

(i) area of cross section = 40 × 60 ₋ π(60 ₋10 ₋ 10)/2 . 1/2

                                     = 1771.6 cm³

(ii) the volume of the concrete slab = 40 × 60 × 120 ₋ 1/2 π((60 ₋ 10   ₋10)/2)² . 120

= 212592 cm³

(iii) The total surface area is:

=40 × 120 × 2 ₊ 60 × 120 ₊ 1771.6 × 2 ₊ 10 × 120 × 2 ₊ 1/2 π(60 ₋ 10 ₋10) × 120

= 30284 cm²

(iv) Mass of the concrete slab given density is 2300 kg/m³

Mass = Volume × density

Mass = 17.716 m³ ×  2300

         = 40746.8 kg/m³

Hence we get the mass as 40746.8 kg/m³.

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