A bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard. Each cone has a base diameter of $ 40 \mathrm{~cm} $ and height $ 1 \mathrm{~m} $. If the outer side of each of the cones is to be painted and the cost of painting is $ Rs.\ 12 $ per $ \mathrm{m}^{2} $, what will be the cost of painting all these cones? (Use $ \pi=3.14 $ and take $ \sqrt{1.04}=1.02) $.
Given:
A bus stop is barricated from the remaining part of the road, by using $50$ hollow cones made of recycled card-board.
Each cone has a base diameter of $40\ cm$ and a height of $1\ m$.
The outer side of each of the cones is to be painted and the cost of painting is $Rs.\ 12$ per $m^2$.
To do:
We have to find the cost of painting these cones.
Solution:
Diameter of the base of the tent $= 40\ cm$
This implies,
Radius of the base of the cone $(r) = \frac{40}{2}$
$=20 \mathrm{~cm}$
$=0.2 \mathrm{~m}$
Height of the cone $(h)=1 \mathrm{~m}$
$=100 \mathrm{~cm}$
Therefore,
Slant height of the cone $(l)=\sqrt{r^{2}+h^{2}}$
$=\sqrt{(20)^{2}+(100)^{2}}$
$=\sqrt{400+10000}$
$=\sqrt{10400} \mathrm{~cm}$
$=102 \mathrm{~cm}$
$=1.02 \mathrm{~m}$
The curved surface area of one cone $=\pi r l$
$=3.14 \times 0.2 \times 1.02$
$=0.64056 \mathrm{~m}^{2}$
The curved surface area of 50 such cones $=0.64056 \times 50$
$=32.028 \mathrm{~m}^{2}$
Rate of painting $= Rs.\ 12$ per $\mathrm{m}^{2}$
Total cost of painting $=Rs.\ 32.028 \times 12$
$=Rs.\ 384.336$
$=Rs.\ 384.34$
Hence,
The total cost of painting these cones is $Rs.\ 384.34$.
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