Question

A unit of area, often used in measuring land areas, is the "hectare", defined as 104 m2. An open-pit coal mine consumes 72 hectares of land, down to a depth of 25 m, each year. What volume of earth, in cubic kilometers, is removed in this time?

Answer 1

Answer:

0.018 km³

Explanation:

Area of land

$A=72\times 10^4\ m^2$

D = Depth of land = 25 m

Volume is given by

$V=AD\\\Rightarrow V=72\times 10^4\times 25\\\Rightarrow V=18000000\ m^3$

Converting to cubic kilometers

$1\ m=\dfrac{1}{1000}\ km$

$1\ m^3=\dfrac{1}{1000^3}\ km^3$

$18000000\ m^3=18000000\times \dfrac{1}{1000^3}=0.018\ km^3$

The volume of Earth removed is 0.018 km³