Question

a solid is composed of a cylinder with hemisherical ends. If the length of the whole solid is 108 cm and the diameter of the cylinder is 36 cm, find the cost of polishing the surface at the rate of 7 paise per cm^2

Answer 1

First work out the surface area of the solid

Area of cylindrical part:-

length of this part = 108 - 2*18 =  72 so its area 

 = 2 * pi * r * 72

=  2 *pi* 18 * 72 =   8143.01 cm^2

Area of the 2 hemispheres = 4 pi  * 18^2 = 4071.50 cm^2

Total surface area of the solid =  12,214.51 cm^2

Cost of polishing = 12,214.51 * 7 =  85,501.58  paise