Q3 of 32 Page 123

If the ratio of radius of base and height of a cone is 5:12 and its volume is 314 cubic metre. Find its perpendicular height and slant height (π = 3.14)

Given: Volume of cone = 314 m3

Radius of base of cone: height of cone = r : h


= 5 : 12


Let radius of base of cone (r) = 5x


And let height of cone (h) = 12x


Volume of cone is given by,


Volume = πr2h/3


Substituting values, we get


314 = (3.14 × (5x)2 × 12x)/3



x3 = 1


x = 1


Thus, radius of the base of cone = 5×1 = 5 m


And height of cone = 12×1 = 12 m


For slant height, we have the relation


l = √(r2 + h2)


l = √(52 + 122)


l = √(25 + 144)


l = √169


l = 13


Hence, we have got perpendicular height of cone to be 12 m and slant height of the cone to be 13 m.


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