Q. 324.8( 11 Votes )

A wooden toy is in the shape of a cone mounted on a cylinder, as shown in the figure. The total height of the toy is 26 cm, while the height of the conical part is 6 cm. The diameter of the base of the conical part is 5 cm and that of the cylindrical part in 4 cm. The conical part and the cylindrical part are respectively painted red and white. Find the area to be painted by each of them colours. [Take π = 22/7.]


Answer :

The wooden toy is in the shape of a cone mounted on a cylinder


Total height of the toy = 26 cm


Height of conical part = H = 6 cm


Height of cylindrical part = Total height of the toy – Height of conical part


h = 26 cm – 6 cm = 20 cm


Diameter of conical part = 5 cm


Radius of conical part = R = Diameter/2 = 5/2 cm = 2.5 cm


Let L be the slant height of the cone


L2 = H2 + R2


L2 = 62 + 2.52 cm2 = 36 + 6.25 cm2 = 42.25 cm2


L = 6.5 cm


Diameter of cylindrical part = 4 cm


Radius of cylindrical part = r = Diameter/2 = 4/2 cm = 2 cm


Area to be painted Red = Curved Surface area of cone + Base area of cone – base area of cylinder


Area to be painted Red = πRL + πR2 – πr2 = π (RL + R2 – r2)


= 22/7 × (2.5 × 6.5 + 2.5 × 2.5 – 2 × 2) cm2


= 22/7 × (16.25 + 6.25 – 4) cm2


= 22/7 × 18.5 cm2


= 58.143 cm2


Area to be painted White = Curved Surface area of cylinder + Base area of cylinder


Area to be painted White = 2πrh + πr2 = πr (2h + r)


= 22/7 × 2 × (2 × 20 + 2) cm2


= 22/7 × 2 × (40 + 2) cm2


= 22/7 × 2 × 42 cm2 = 264 cm2


Area to be painted red is 58.143 cm2 and area to be painted white is 264 cm2.


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