Question

A cylinder has hemispherical ends having radius $7$ cm and total height of solid is $104$ cm. If its outer surface is to be polished and cost of polish is rs $100$ per.sq.mtr find the total cost of polish.

Answer 1

Let $AD=104cm$

$AB=CD=r=7cm$

$BC=h=90cm$

Surface area of cylindrical part $=2\times \pi \times r\times h=2\times \pi \times 7\times h=3958.41c{m}^2=0.396m^2$

Surface area of one hemispherical end $=2\times \pi \times r\times r=2\times \pi \times 7\times 7=307.88c{m}^2=0.031m^2$

Total surface area $=0.396+(0.031\times 2)=0.458m^2$

Cost of polish per square metre $=100Rs$

Cost of polishing total surface area $=45.8Rs$