In this post, we will share NCERT Class 10th Maths Book Solutions Chapter 13 Surface Areas and Volumes Ex 13.2 class 10 maths. These solutions are based on new NCERT Syllabus.

## Chapter 13 Surface Areas and Volumes Ex 13.2 Class 10 Maths

Unless stated otherwise, take π = \(\frac{22}{7}\)

Ex 13.2 class 10 maths 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.

Solution:

Here, r = 1 cm and h = 1 cm.

Volume of the conical part = \(\frac{1}{3}\) πr^{2}h and volume of the hemispherical part = \(\frac{2}{3}\) πr^{3}h

∴ Volume of the solid shape

= \(\frac{1}{3}\) πr^{2}h + \(\frac{2}{3}\) πr^{3}h = \(\frac{1}{3}\) πr^{2}h[h + 2r]

= \(\frac{1}{3}\) π(1)^{2} [1 + 2(1)] cm^{3}

= (\(\frac{1}{3}\) π × 1 × 3) cm^{3} = π cm^{3}

Ex 13.2 class 10 maths 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.)

Solution:

Here, diameter = 3 cm

⇒ Radius (r) = \(\frac{3}{2}\) cm

Total height = 12 cm

Height of a cone (h_{1}) = 2 cm

∴ Height of both cones = 2 × 2 = 4 cm

⇒ Height of the cylinder (h_{2}) = (12 – 4) cm = 8 cm.

Now, volume of the cylindrical part = πr^{2}h_{2}

Volume of both conical parts = 2[\(\frac{1}{3}\) πr^{2}h_{1}]

∴ Volume of the whole model

Ex 13.2 class 10 maths 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 figure).

Solution:

Since a gulab jamun is like a cylinder with hemispherical ends.

Total height of the gulab jamun = 5 cm.

Diameter = 2.8 cm

⇒ Radius (r) = 1.4 cm

∴ Length of the cylindrical part (h)

= 5 cm – (1.4 + 1.4) cm = 5 cm – 2.8 cm = 2.2 cm

Now, volume of the cylindrical part = πr^{2}h and volume of both the hemispherical ends

= 2(\(\frac{2}{3}\) πr^{3}) = \(\frac{4}{3}\) πr^{3}

∴ Volume of a gulab jamun

Volume of 45 gulab jamuns

Ex 13.2 class 10 maths Question 4.

A pen stand made up 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 figure).

Solution:

Dimensions of the cuboid are 15 cm by 10 cm by 3.5 cm.

∴ Volume of the cuboid = 15 × 10 × \(\frac{35}{10}\) cm^{3}

= 525 cm^{3}

Since, each depression is conical in shape with base radius (r) = 0.5 cm and depth (h) = 1.4 cm

∴ Volume of each depression

= \(\frac{1}{3} \pi r^{2} h=\frac{1}{3} \times \frac{22}{7} \times\left(\frac{5}{10}\right)^{2} \times \frac{14}{10} \mathrm{cm}^{3}=\frac{11}{30} \mathrm{cm}^{3}\)

Since, there are 4 depressions

∴ Total volume of 4 depressions = \(\frac{44}{30}\) cm^{3}

Now, volume of the wood in entire stand = [Volume of the wooden cuboid] – [Volume of 4 depressions]

= 525cm^{3} – \(\frac{44}{30}\) cm^{3}

= \(\frac{15750-44}{30} \mathrm{cm}^{3}=\frac{15706}{30} \mathrm{cm}^{3}\)

= 523.53 cm^{3}

Ex 13.2 class 10 maths 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.

Solution:

Height of the conical vessel (h) = 8 cm

Base radius (R) = 5 cm

Volume of water in conical vessel = \(\frac{1}{3}\) πR^{2}h

Thus, the required number of lead shots = 100

Ex 13.2 class 10 maths 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 cm^{3} of iron has approximately 8 g mass. (Use π = 3.14)

Solution:

Height of the big cylinder (h) = 220 cm

Base radius (r) = \(\frac{24}{2}\) cm = 12cm

∴ Volume of the big cylinder

= πr^{2}h = (π(12)^{2} × 220) cm^{3}

Also, height of smaller cylinder (h_{1}) = 60 cm

Base radius (r_{1}) = 8 cm

∴ Volume of the smaller cylinder πr_{1}^{2}h_{1}

= (π(8)^{2} × 60) cm^{3}

∴ Volume of iron pole = [Volume of big cylinder] + [Volume of the smaller cylinder]

= (π × 220 × 12^{2} × π × 60 × 8^{2}) cm^{3}

= 3.14[220 × 12 × 12 + 60 × 8 × 8] cm^{3}

Ex 13.2 class 10 maths 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.

Solution:

Height of the conical part = 120 cm

Base radius of the conical part = 60 cm

Volume of the conical part

= \(\frac{1}{3}\) πr^{2}h = [\(\frac{1}{3} \times \frac{22}{7}\) × (60)^{2} × 120] cm^{3}

Radius of the hemispherical part = 60 cm.

Ex 13.2 class 10 maths 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 cm^{3}. Check whether she is correct, taking the above as the inside measurements, and π = 3.14.

Solution:

Volume of the cylindrical part = πr^{2}h

= (3.14 × 1^{2} × 8) cm^{3} = \(\frac{314}{100}\) × 8 cm^{3}

∴ Total volume of the glass vessel = [Volume of cylindrical part] + [Volume of spherical part]

⇒ Volume of water in the vessel = 346.51 cm^{3}

Since the child finds the volume as 345 cm^{3}

∴ The child’s answer is not correct.

The correct answer is 346.51 cm^{3}.