Question

How many cubic metres of earth must be dug to construct a well 7 m deep and of diameter 2.8 m?

Answer 1

Answer:

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:4.8

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 =

=

= 770 m3

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

Therefore,

Height =

=

= 2.5

Answer 2

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Height = 7m

Diameter = 2.8 m

Then, radius = 2.8/2 m = 1.4 m

Now

Volume of cylinder =¶r²h

= 22/7×1.4×1.4×7 m

= 22×1.4×1.4 m³

= 43.12 m³

Thus, 43.12 m³ of earth must be dug to construct a well 7 m deep and of diameter 2.8 m.

$\boxed{Hope\:This\:Helps}$

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