Question

How many cubic metres of earth must be dug out to sink a well which is 20 m deep and has a diameter of 7 metres? If the earth so dug out is spread over a rectangular plot 28 m by 11 m, what is the height of the platform so formed?

Answer 1

It is given in the question that, 

Diameter = 7m 

Hence, 

Radius = 3.5 m 

Depth = 20 m 

Volume of the earth to be dug out = \(\pi r^2h\)

= \(\frac{22}{7}\times3.5\times3.5\times20\)

= 770 m³

Volume of the earth piled upon the given plot = 28× 11 × h 

Therefore,

Height = \(\frac{770}{28\times11}\)

= \(\frac{70}{28}\)

= 2.5 m