5. A metallic right circular cone 20 cm high and whose vertical angle is 60° is cut into two
parts at the middle of its height by a plane parallel to its base. If the frustum so obtained
be drawn into a wire of diameter - cm, find the length of the wire.
16.
Answers
Answer:
7964.4 m
Step-by-step explanation:
Let R be the radius of the base of the cone and r be the radius of the upper of frustum.
Then,
In triangle ABG
______
In triangle ADF
________
Height of the frustum, h =10cm (given)
Volume of the used in frustum
_______
Now the radius of wire = 1/32 cm
Let l be the length of the wire.
Then the volume of the cylindrical wire = volume of metal used in frustum.
Therefore : length of the wire is 7964.4m
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7964.4 m
Let R be the radius of the base of the cone and r be the radius of the upper of frustum.
Then,
In triangle ABG
\tan(30) = \frac{R \: }{AG \: }tan(30)=AGR
$$\begin{lgathered}\frac{1}{ \sqrt{3} } = \frac{R \: }{20} \\ \\ R = \frac{20}{ \sqrt{3} } \\ \\ R = \frac{20 \sqrt{3} }{3}\end{lgathered}$$
______
In triangle ADF
$$\begin{lgathered}\tan(30) = \frac{r \: }{AF \: } \\ \\ \frac{1}{ \sqrt{3} } = \frac{r}{10} \\ \\ r = \frac{10}{ \sqrt{3} } \\ \\ r = \frac{10 \sqrt{3} }{3} \:\end{lgathered}$$
________
Height of the frustum, h =10cm (given)
Volume of the used in frustum
$$= \frac{1}{3} \pi \: h( {R}^{2} + {r}^{2} +R r)$$
$$\begin{lgathered}= \frac{1}{3} \pi \times 10( {( \frac{20 \sqrt{3} }{3} \: )}^{2} + ( \frac{ {10 \sqrt{3} }^{2} }{3} ) + \frac{20 \sqrt{3} \times 10 \sqrt{3} }{3} ) \\ \\ = \frac{1}{3} \pi \times 10( \frac{400}{3} + \frac{100}{3} + \frac{200}{3} ) \\ \\ = \frac{7000}{9} \pi \: {cm}^{3} \\ \\\end{lgathered}$$
_______
Now the radius of wire = 1/32 cm
Let l be the length of the wire.
Then the volume of the cylindrical wire = volume of metal used in frustum.
$$\begin{lgathered}\pi { \frac{1}{32} }^{2} \times l = \frac{7000}{9} \pi \\ \\ l = \frac{7000 \times 32 \times 32}{9} \\ \\ l = \frac{7168000}{9} cm \\ \\ l = \frac{7168000}{9 \times 100} \\ \\ = 7964.4m\end{lgathered}$$
Therefore : length of the wire is 7964.4m
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