Question

Fig. 15.18 shows the plan of a foundation

which is of uniform width 1 m.

If 1 m³of earth has a mass of 1½ tonnes, what
mass of earth will be removed when digging
the foundation to a depth of 1½m? ​

Answer 1

121.5 tonnes of earth will be removed

Explanation:

The first thing to do here is to calculate the area of this shape.

We can see that we have three different rectangles here

So the area of the shape is the sum of the areas of the rectangles

This will be;

(18 * 1) + (13 * 1) + (23 * 1) = 18 + 13 + 23 = 54 m^2

Wondering how we got 23?

You know the total top length is 25, removing 1n from each side leaving the central value will

give a rectangle of 23 by 1

Now, digging the foundation to a depth of 1.5m

The volume dug will be = area of shape * depth of digging = 54 * 1.5 = 81 m^3

Now, 1 m^3 has mass of 1.5 tones, 81 m^3 will have a mass of 81 * 1.5 = 121.5 tonnes