A rocket is in the form of a right circular cylinder closed at the lower end and surmounted by a cone with the same radius as that of the cylinder. The diameter and height of the cylinder are 6 cm and 12 cm, respectively. If the slant height of the conical portion is 5 cm, then find the total surface area and volume of the rocket.


The diagram is given as:


For upper conical part,


Radius of base, r = 3 cm


Slant height, l = 5 cm


As,


l2 = h2 + r2, where h , r and l are height radius respectively.


h2 = l2 - r2


h2 = (5)2 - (3)2


h2= 25 - 9 = 16


h = 4 cm


Also,


volume of cone


Curved surface area of cone = πrl = π(3)(5) = 15π cm2


For cylindrical part,


Radius of base = Radius of base of conical part = r = 3 cm


Height, h = 12 cm


Also,


Volume of cylinder = πr2h = π(3)2(12) = 108π cm3


Curved surface area of cylinder = 2πrh = 2π(3)(12) = 72π cm2


Volume of rocket = volume of conical part + volume of cylindrical part


Volume of rocket = 12π + 108π = 120π



Also,


Surface area of rocket = Curved surface area of conical part + Curved surface area of Cylindrical part + Surface area of base of rocket


Surface area of base of rocket = πr2 = π(3)2 = 9π cm2


Therefore,


Surface area of rocket = 15π + 72π + 9π = 94π cm2



14
1