Question

A solid is composed of a cylinder with hemispherical ends. If the length of the whole solid is $108cm$ and the diameter of the cylinder is $36cm$, find the cost of polishing the surface at the rate of $7$ paise per ${cm}^2$. (Use $\pi =3.1416$)

Answer 1

CSA of solid$=2\pi rh+2\times 2\pi r^2=2\pi r(h+2r)$

$=2\times 3.1416\times 18((108-2\times 18)+2\times 18)$

$=2\times 3.1416\times 18\times 108=12214.5408㎠$

Cost of polishing=Rs.$(12214.5408\times 0.07)$=Rs.$855.02$