Answer :


Let ‘R’ be the radius of the base of the cone which is also the base of frustum i.e. lower circular end as shown in the figure


DE = R


Let ‘r’ be the radius of the upper circular end of frustum which we get after cutting the cone


BC = r


The height of the cone is 20 cm and we had cut the cone at midpoint therefore height of the frustum so obtained is 10 cm


Vertical angle as shown in the figure is 60˚


Now a wire of diameter 1/12 (i.e. radius 1/24) is made out of the frustum let ‘l’ be the length of the wire


As we are using the full frustum to make wire therefore volumes of both the frustum and the wire must be equal.


Volume of frustum = volume of wire made …(i)


Consider ΔABC


BAC = 30˚ ; AB = 10 cm ; BC = r



r = 10/√3 cm


Consider ΔADE


DAE = 30˚ ; AD = 20 cm ; DE = R



R = 20/√3 cm


Now using equation (i)





7000/9 = l/576


777.778 = l/576


l = 448000 cm


Length of wire = 448000 cm

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