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Q.

A well with 14 m diameter is dug 8 m deep. The earth taken out of it has been evenly spread all around it to a width of 21 m to form an embankment. Find the height of the embankment.


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a

53 cm

b

54 cm

c

64 cm

d

73 cm 

answer is A.

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Detailed Solution

It is given a well of diameter 14 m and depth 8 m, width of the embankment is 21 m.
Given,  Question Image Since, radius= Diameter 2    So, radius(r) ,
r= 14 2 r=7 m   Volume = π r 2 h  
  V= 22 7 × 7 2 ×8  
V= 22 7 ×7×7×8  
V=1232 m 3   Now, width of embankment = 21 m
Inner radius = Radius of a cylindrical well = 7m
Outer radius = Width of embankment + Radius of cylindrical well
  Outer radius = 21m+7m
  Outer radius = 28m
Since, area of the material contained in a hollow cylindrical shell = π R 2 r 2   So, area of the embankment,
Area of the embankment=π R 2 r 2  
Area of the embankment= 22 7 28 2 7 2  
Area of the embankment= 22 7 28+7 287  
Area of the embankment= 22 7 ×35×21  
Area of the embankment=2310 m 2   Since, volume of the embankment = Area of embankment ×   Height of embankment
  Volume of the embankment=π R 2 r 2 h   And volume of embankment = Volume of the earth that dugout = 1232 m 3  
So, height of embankment =  Volume of embankment Area of embankment  
Height of embankment= 1232 2310 Height of embankment=0.53m  
We know that, 1m = 100 cm  
So, 0.53m = 53cm
Therefore, the height of the embankment is 53 cm  .
Hence option (1) is correct.
 
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