Question

A solid is composed of a cylinder with hemispherical ends. If the length of the cylindrical part is $104cm$ and the radius of each of the hemispherical ends is $7cm$, find the cost of polishing its surface at the rate of Rs. $10$ per ${dm}^2$.

Answer 1

Total area of polishing = CSA of cylinder + 2$\times$ CSA of hemisphere

Given: $r=7cm,h=104cm$

Therefore,

$SurfaceArea=2\pi rh+2\times 2\pi r^2$

$A=2\pi \times 7\times 104+4\pi \times 7^2$

$A=5190c{m}^2=51.9d{m}^2$ {$1dm=10cm$}

Cost of polishing$=51.9\times 10=519Rs.$