# From a Cubical Piece of Wood of Side 21 Cm, a Hemisphere is Carved Out in Such a Way that the Diameter of the Hemisphere is Equal to the Side of the Cubical Piece. Find the Surface Area - Mathematics

Sum

From a cubical piece of wood of side 21 cm, a hemisphere is carved out in such a way that the diameter of the hemisphere is equal to the side of the cubical piece. Find the surface area and volume of the remaining piece.

#### Solution

We have,

the edge of the cubical piece, a = 21 cm and

the radius of the hemisphere, r = a/2=21/2

The surface area of the remaining piece = TSA of cube + CSA of hemisphere -Area of

= 6a2 + 2πr2 - πr

= 6a2 + πr2

= 6 xx 21xx21xx22/7xx21/5xx21/2

= 21xx21(6 + 22/(7+4))

= 21xx21(6+11/14)

=21xx21((84+11)/14)

= 21xx3(95/2)

= 2992.5 cm2

Also,

Volume of the remaining piece = volume of the cube - volume of the hemisphere

= a^3 - 2/3pir^3

= 21xx21xx21 - 2/3xx22/7xx(21/2)xx(21/2)xx(21/2)

= 21xx21xx21xx(1-2/3xx22/7xx1/2xx1/2xx1/2)

= 21xx21xx21(1/1 - 11/42)

=21xx21xx21xx(42-11)/42

= 21xx21xx(31/2)

= 6835.5 cm3

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#### APPEARS IN

RS Aggarwal Secondary School Class 10 Maths
Chapter 19 Volume and Surface Area of Solids
Exercise 19A | Q 28 | Page 877