Question

Find the cost of painting the outside surface of a solid cylinder of diameter $7m$ and height $20m$ at Rs 5 per $m^2$.

Answer 1

Diameter of the solid cylinder $=7m$

Radius of the solid cylinder $=\frac{7}{2}=3.5m$

Height of the solid cylinder $=20m$

Painting the outer surface of the cylinder$=$Total surface area of the cylinder

$\Rightarrow$Total surface area of the cylinder$=2\pi r(r+h)$

$=2\times \frac{22}{7}\times 3.5\times (3.5+20)$

$=\frac{22}{7}\times 7\times 23.5$

$=22\times 23.5=517sq.m$

Cost to paint $1sq.m=Rs.5$

Cost to paint $517sq.m=Rs.5\times 517=Rs.2,585$