Q20 of 34 Page 1

A wooden souvenir is made by scooping out a hemisphere from each end of a solid cylinder. If the height of the cylinder is 10 cm and its base is of radius 3.5 cm then find the total cost of polishing the souvenir at the rate of Rs. 10 per cm2.

Total area to be polished = CSA of cylinder + 2(CSA of scooped out hemispheres)


Radius of cylinder = Radius of hemisphere = r = 3.5 cm


Height of cylinder, h = 10 cm


Also, CSA of cylinder = 2πrh


Where, r is base radius and h is height of cylinder.


CSA of hemisphere of radius r = 2πr2


Therefore,


Total area to be polished = 2πrh + 2(2πr2)


= 2πr(h + 2r)



= 374 cm2


Cost of polishing for 1 cm2= 10 Rs


Cost of polishing for 374 cm2 = 3740 Rs


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