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EXERCISE 13.1

Unless stated otherwise, take π =
22
7

**Question 1.** 2 cubes each of volume 64 cm3 are joined end to end. Find the surface area of the
resulting cuboid.

**Question 2.** A vessel is in the form of a hollow hemisphere mounted by a hollow cylinder. The
diameter of the hemisphere is 14 cm and the total height of the vessel is 13 cm. Find the
inner surface area of the vessel.

**Question 3.** A toy is in the form of a cone of radius 3.5 cm mounted on a hemisphere of same radius.
The total height of the toy is 15.5 cm. Find the total surface area of the toy.

**Question 4.** A cubical block of side 7 cm is surmounted by a hemisphere. What is the greatest
diameter the hemisphere can have? Find the surface area of the solid.

**Question 5.** A hemispherical depression is cut out from one face of a cubical wooden block such
that the diameter l of the hemisphere is equal to the edge of the cube. Determine the
surface area of the remaining solid.

**Question 6.** A medicine capsule is in the shape of a
cylinder with two hemispheres stuck to each
of its ends (see Fig. 13.10). The length of
the entire capsule is 14 mm and the diameter
of the capsule is 5 mm. Find its surface area.

**Question 7.** A tent is in the shape of a cylinder surmounted by a conical top. If the height and
diameter of the cylindrical part are 2.1 m and 4 m respectively, and the slant height of the
top is 2.8 m, find the area of the canvas used for making the tent. Also, find the cost of
the canvas of the tent at the rate of Rs 500 per m2. (Note that the base of the tent will not
be covered with canvas.)

**Question 8.** From a solid cylinder whose height is 2.4 cm and diameter 1.4 cm, a conical cavity of the
same height and same diameter is hollowed out. Find the total surface area of the
remaining solid to the nearest cm2.

**Question 9. **A wooden article was made by scooping
out a hemisphere from each end of a solid
cylinder, as shown in Fig. 13.11. If the
height of the cylinder is 10 cm, and its
base is of radius 3.5 cm, find the total
surface area of the article.

EXERCISE 13.2

Unless stated otherwise, take π =
22
/7 .

**Question 1.** A solid is in the shape of a cone standing on a hemisphere with both their radii being
equal to 1 cm and the height of the cone is equal to its radius. Find the volume of the solid
in terms of π.

**Question 2.** Rachel, an engineering student, was asked to make a model shaped like a cylinder with
two cones attached at its two ends by using a thin aluminium sheet. The diameter of the
model is 3 cm and its length is 12 cm. If each cone has a height of 2 cm, find the volume
of air contained in the model that Rachel made. (Assume the outer and inner dimensions
of the model to be nearly the same.)

**Question 3.** A gulab jamun, contains sugar syrup up to about
30% of its volume. Find approximately how much
syrup would
be found in 45 gulab jamuns, each
shaped like a cylinder with two hemispherical ends
with length 5 cm and diameter 2.8 cm (see Fig. 13.15).

**Question 4. **A pen stand made of wood is in the shape of a
cuboid with four conical depressions to hold pens.
The dimensions of the cuboid are 15 cm by 10 cm by
3.5 cm. The radius of each of the depressions is 0.5
cm and the depth is 1.4 cm. Find the volume of
wood in the entire stand (see Fig. 13.16).

**Question 5.** A vessel is in the form of an inverted cone. Its
height is 8 cm and the radius of its top, which is
open, is 5 cm. It is filled with water up to the brim.
When lead shots, each of which is a sphere of radius
0.5 cm are dropped into the vessel, one-fourth of
the water flows out. Find the number of lead shots
dropped in the vessel.

**Question 6.** A solid iron pole consists of a cylinder of height 220 cm and base diameter 24 cm, which
is surmounted by another cylinder of height 60 cm and radius 8 cm. Find the mass of the
pole, given that 1 cm3 of iron has approximately 8g mass. (Use π = 3.14)

**Question 7.** A solid consisting of a right circular cone of height 120 cm and radius 60 cm standing on
a hemisphere of radius 60 cm is placed upright in a right circular cylinder full of water
such that it touches the bottom. Find the volume of water left in the cylinder, if the radius
of the cylinder is 60 cm and its height is 180 cm.

**Question 8.** A spherical glass vessel has a cylindrical neck 8 cm long, 2 cm in diameter; the diameter
of the spherical part is 8.5 cm. By measuring the amount of water it holds, a child finds its
volume to be 345 cm3. Check whether she is correct, taking the above as the inside
measurements, and π = 3.14

EXERCISE 13.3

Take π =
22
7 , unless stated otherwise.

**Question 1.** A metallic sphere of radius 4.2 cm is melted and recast into the shape of a cylinder of
radius 6 cm. Find the height of the cylinder.

**Question 2.** Metallic spheres of radii 6 cm, 8 cm and 10 cm, respectively, are melted to form a single
solid sphere. Find the radius of the resulting sphere.

**Question 3.** A 20 m deep well with diameter 7 m is dug and the earth from digging is evenly spread out
to form a platform 22 m by 14 m. Find the height of the platform.

**Question 4.** A well of diameter 3 m is dug 14 m deep. The earth taken out of it has been spread evenly
all around it in the shape of a circular ring of width 4 m to form an embankment. Find the
height of the embankment.

**Question 5.** A container shaped like a right circular cylinder having diameter 12 cm and height 15 cm
is full of ice cream. The ice cream is to be filled into cones of height 12 cm and diameter
6 cm, having a hemispherical shape on the top. Find the number of such cones which can
be filled with ice cream.

**Question 6.** How many silver coins, 1.75 cm in diameter and of thickness 2 mm, must be melted to form
a cuboid of dimensions 5.5 cm × 10 cm × 3.5 cm?

**Question 7.** A cylindrical bucket, 32 cm high and with radius of base 18 cm, is filled with sand. This
bucket is emptied on the ground and a conical heap of sand is formed. If the height of the
conical heap is 24 cm, find the radius and slant height of the heap.

**Question 8.** Water in a canal, 6 m wide and 1.5 m deep, is flowing with a speed of 10 km/h. How much
area will it irrigate in 30 minutes, if 8 cm of standing water is needed?

**Question 9.** A farmer connects a pipe of internal diameter 20 cm from a canal into a cylindrical tank in
her field, which is 10 m in diameter and 2 m deep. If water flows through the pipe at the
rate of 3 km/h, in how much time will the tank be filled?

EXERCISE 13.4

Use π =
22
7 unless stated otherwise.

**Question 1.** A drinking glass is in the shape of a frustum of a
cone of height 14 cm. The diameters of its two
circular ends are 4 cm and 2 cm. Find the capacity of
the glass.

**Question 2.** The slant height of a frustum of a cone is 4 cm and
the perimeters (circumference) of its circular ends
are 18 cm and 6 cm. Find the curved surface area of
the frustum.

**Question 3.** A fez, the cap used by the Turks, is shaped like the
frustum of a cone (see Fig. 13.24). If its radius on the
open side is 10 cm, radius at the upper base is 4 cm
and its slant height is 15 cm, find the area of material
used for making it.

**Question 4.** A container, opened from the top and made up of a metal sheet, is in the form of a
frustum of a cone of height 16 cm with radii of its lower and upper ends as 8 cm and 20
cm, respectively. Find the cost of the milk which can completely fill the container, at the
rate of Rs 20 per litre. Also find the cost of metal sheet used to make the container, if it
costs Rs 8 per 100 cm2. (Take π = 3.14)

**Question 5.** A metallic right circular cone 20 cm high and whose vertical angle is 60° is cut into two
parts at the middle of its height by a plane parallel to its base. If the frustum so obtained
be drawn into a wire of diameter 1 cm,
16
find the length of the wire.

EXERCISE 13.5 (Optional)*

**Question 1.** A copper wire, 3 mm in diameter, is wound about a cylinder whose length is 12 cm, and
diameter 10 cm, so as to cover the curved surface of the cylinder. Find the length and
mass of the wire, assuming the density of copper to be 8.88 g per cm3.

**Question 2.** A right triangle, whose sides are 3 cm and 4 cm (other than hypotenuse) is made to
revolve about its hypotenuse.
Find the volume and surface area of the double cone so
formed. (Choose value of π as found appropriate.)

**Question 3.** A cistern, internally measuring 150 cm × 120 cm × 110 cm, has 129600 cm3 of water in it.
Porous bricks are placed in the water until the cistern is full to the brim. Each brick
absorbs one-seventeenth of its own volume of water. How many bricks can be put in
without overflowing the water, each brick being 22.5 cm × 7.5 cm × 6.5 cm?

**Question 4.** In one fortnight of a given month, there was a rainfall of 10 cm in a river valley. If the area
of the valley is 97280 km2, show that the total rainfall was approximately equivalent to
the addition to the normal water of three rivers each 1072 km long, 75 m wide and 3 m
deep.

**Question 5.** An oil funnel made of tin sheet consists of a
10 cm long cylindrical portion attached to a
frustum of a cone. If the total height is 22 cm,
diameter of the cylindrical portion is 8 cm and
the diameter of the top of the funnel is 18 cm,
find the area of the tin sheet required to make
the funnel (see Fig. 13.25).

**Question 6.** Derive the formula for the curved surface area and total surface area of the frustum of a
cone, given to you in Section 13.5, using the symbols as explained.

**Question 7.** Derive the formula for the volume of the frustum of a cone, given to you in Section 13.5,
using the symbols as explained.

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- Chapter 1: REAL NUMBERS
**[Ques wise Ans]** - Chapter 2: POLYNOMIALS
**[Ques wise Ans]** - Chapter 3: PAIR OF LINEAR EQUATIONS IN TWO VARIABLE
**[Ques wise Ans]** - Chapter 6: Triangles
**[Ques wise Ans]** - Chapter 3 Pair of Linear Equations in Two Variables
- Chapter 4 Quadratic Equations
- Chapter 7 Coordinate Geometry
- Chapter 8 Introduction to Trigonometry
- Chapter 11 Constructions
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- Chapter 12 Areas Related to Circles
- Chapter 13 Surface Areas and Volumes
- Chapter 14 Statistics
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- Chapter 5 Arithmetic Progressions

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