A well of inner diameter 14 m is dug to a depth of 12 m. Earth taken out of it has been evenly spread all around it to a width of 7 m to form an embankment. Find the height of the embankment so formed.
Hint. Required height =
Given that,
Inner diameter = 14 cm
Therefore,
Radius = 7 cm
Also, Depth = 12 m
Therefore,
Volume of earth dug out = 
r2h
= 
= 1848 m3
It is also given that,
Width of embankment = 7 m
Therefore,
Total radius = 7 + 7 = 14 m
Volume of embankment = Total volume – Inner volume
= 
ro2h – 
r12h
= 
h (ro2 – r12)
= 
h (142 - 72)
= 
h (196 – 49)
= 
× 147
= 21 × 22h
= 462 × h m3
Since,
Volume off embankment = Volume of earth dug out
Therefore,
1848 = 462 h
h = 
h = 4 m
Therefore,
Height of the embankment = 4 m
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