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0 votes
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in Mensuration by (35.6k points)
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An iron spherical ball of volume 232848 cm3 has been melted and converted into a cone with vertical angle of 120°. Then the height of the cone is

A) 42√3 cm 

B) 42 cm 

C) 21 cm 

D) None

2 Answers

+1 vote
by (66.4k points)
selected by
 
Best answer

Correct option is: B) 42 cm

Let radius and height of the cone be r and h respectively.

Given that vertical angle of cone is \(120^\circ\).

i.e \(\angle CBA = 120^\circ\)

\(\Rightarrow\) \(\angle ABO = \frac {\angle CBA}{2} = \frac {120^\circ}{2} = 60^\circ\)

In right \(\triangle AOB\),

\(\frac {OA}{OB} = tan \, 60^\circ = \sqrt3\)

\(\Rightarrow\) \(\frac rh = \sqrt3\)

\(\Rightarrow\) r = \(h\sqrt3\)

Volume of cone = volume of spherical ball

\(\Rightarrow\) \(\frac 13 \pi r^2h\) = 232848

\(\Rightarrow\) \(\frac 13 \pi \times 3h^3\) = 232848

\(\Rightarrow\) \(h^3 = \frac {232848}\pi= \frac {232848\times7}{22}\) = 10584 \(\times\) 7 = 74088 = \(42^3\)

\(\therefore\) h = 42 cm.

Hence, the height of the cone is 42 cm.

+1 vote
by (34.5k points)

Correct option is: A) 42√3 cm

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