Question

calculate the surface area of a conical bedside lamp whose top and bottom diameter 18 cm and 30 cm respectively and the practical height is 4 cm​

Answer 1

Given: Height of the frustrum (h)=24 cm

radius of lower end of bucket (r

1

)=

2

10

=5cm

Radius of upper end of bucket (r

2

)=

2

30

=15cm

∴ Slant height (l)=

h

2

+(r

2

−r

1

)

2

=

(24)

2

+(15−5)

2

=

(24)

2

+(10)

2

=

576+100

=

676

=26cm

Now, Area of the metal sheet used to make the bucket = T.S.A of the

bucket (excluding the upper end)

Total Surface Area(TSA) =π(r

1

+r

2

)l+πr

1

2

=(3.14)(15+5)(26)+3.14(5)

2

=1632.8+78.5=1711.3cm

2

(b) We should avoid the bucket made by ordinary plastic as plastic is non biodegradable and hazardous to environment.