Posted by liz on Wednesday, August 25, 2010 at 6:17pm.
A unit of area often used in measuring land areas is the hectare, defined as 104 m2. An openpit coal mine consumes 72 hectares of land, down to a depth of 29 m, each year. What volume of earth, in cubic kilometers, is removed in this time?

physics  MathMate, Wednesday, August 25, 2010 at 7:24pm
The volume of earth removed is a rectangular prism, the volume of which is the planar area multiplied by the depth.
V = 72 hectares * 29 m
= 72*104 m² * 29 m
= 72*104*29 m³
Now one cubic kilometer contains
(1000)³ m³
= 1,000,000,000 m³
All you need to do is to convert the previous answer into km³. 
physics  Mike, Friday, September 3, 2010 at 5:02pm
.0207 km3