All questions of Surface Area and Volume for Class 10 Exam

On increasing each of the radius of the base and the height of a cone by 20%. By what percent its volume will be increased?
  • a)
    72.8%
  • b)
    60%
  • c)
    40%
  • d)
    30%
Correct answer is option 'A'. Can you explain this answer?

Let the original radius be r and height be h.
Original volume = V = 1/3 πr2h
New radius = 120% of r = 120r/100 = 6r/5
New height = 120% of h = 120h/100 = 6h/5
New volume

Increase in volume 

Increase %

A tent is in the shape of a right circular cylinder up to a height of 3 m and then becomes a right circular cone with a maximum height of 13.5 m above the ground. Calculate the cost of painting the inner side of the tent at the rate of ₹ 2 per m2, if the radius of the base is 14 m.
  • a)
    ₹ 2068
  • b)
    ₹ 2156 
  • c)
    ₹ 2248
  • d)
    ₹ 1872
Correct answer is option 'A'. Can you explain this answer?

Vivek Bansal answered
Radius of cylinder = Radius of cone = 14 m. 
Height of cylinder = 3 m
Height of cone = 10.5 m 
Slant height of cone
Total curved surface area of tent = Curved surface area of cylinder + Curved surface area of cone
= π(2x14x3 + 14x17.5)
Cost of painting the inner surface at the rate of ₹ 2 per m2 = 2 x 1034 =₹ 2068

A sector of a circle of radius 12 cm has the angle 120°. It is rolled up so that two bounding radii are joined together to form a cone. Find the volume of the cone.
  • a)
    189.61 cm3
  • b)
    169.51 cm3
  • c)
    179.61 cm3
  • d)
    125.51 cm3
Correct answer is option 'A'. Can you explain this answer?

Bhavana Kaur answered
To find the area of a sector, you can use the formula:

Area of sector = (θ/360) * π * r^2

where θ is the angle in degrees and r is the radius.

In this case, the radius is given as 12 cm and the angle is 120 degrees. Plugging these values into the formula, we get:

Area of sector = (120/360) * π * 12^2
= (1/3) * π * 144
= 48π cm^2

So, the area of the sector is 48π cm^2.

The ratio between the volume of two sphere is 8 : 27. What is the ratio between their surface areas?
  • a)
    4 : 9
  • b)
    4 : 5
  • c)
    5 : 6
  • d)
    4 : 7
Correct answer is option 'A'. Can you explain this answer?

Sheena mehta answered
Given:
The ratio between the volume of two spheres is 8: 27.

To find:
The ratio between their surface areas.

Solution:
Let's consider two spheres with volumes V1 and V2, and surface areas S1 and S2 respectively.

Step 1:
We know that the volume of a sphere is given by the formula:
V = (4/3)πr³, where r is the radius of the sphere.

So, the given ratio between the volumes can be written as:
V1/V2 = 8/27

Step 2:
Let's assume the radii of the two spheres as r1 and r2 respectively.

Therefore, we can write the volumes as:
V1 = (4/3)πr1³
V2 = (4/3)πr2³

Step 3:
Now, let's simplify the given ratio using the expressions for volumes:
(4/3)πr1³ / (4/3)πr2³ = 8/27

The π and (4/3) terms cancel out on both sides, leaving us with:
(r1/r2)³ = 8/27

Step 4:
Taking the cube root of both sides, we get:
r1/r2 = 2/3

Step 5:
We know that the surface area of a sphere is given by the formula:
S = 4πr²

Substituting the radii r1 and r2, we can write the surface areas as:
S1 = 4πr1²
S2 = 4πr2²

Step 6:
Now, let's find the ratio between the surface areas:
S1/S2 = (4πr1²) / (4πr2²)
S1/S2 = (r1²/r2²)

Step 7:
Using the ratio r1/r2 = 2/3 from Step 4, we can substitute it into the above expression:
S1/S2 = (2/3)²
S1/S2 = 4/9

Conclusion:
Therefore, the ratio between the surface areas of the two spheres is 4:9.
Hence, the correct answer is option A) 4:9.

A box opened at the top has its outer dimensions 10 cm × 9 cm × 2.5 cm and its thickness is 0.5 cm, find the volume of the metal.
  • a)
    92.5 cm3
  • b)
    72 cm3
  • c)
    63.5 cm3
  • d)
    81 cm3
Correct answer is option 'D'. Can you explain this answer?

Ritu Saxena answered
Outer dimension s of the box are 10 cm, 9 cm and 2.5 cm.
Thickness of the box is 0.5 cm.
So, inner dimensions of the box is (10 - 2 x 0.5) cm,
(9 - 2 x 0.5) cm and (2.5 - 0.5) cm
i.e, 9 cm, 8 cm and 2 c
Volume of the metal = Volume of outer box - Volume of inner box
= 10 x 9 x 2.5 - 9 x 8 x 2 = 225 - 144 = 81 cm3

The weight of a metallic spherical shell is 11.176 kg. If the inner radius of the cell is 6 cm. 1 cm3 of the metal weights 21 g then what is the thickness of the shell?
  • a)
    1 cm
  • b)
    2 cm
  • c)
    3 cm
  • d)
    4 cm
Correct answer is option 'A'. Can you explain this answer?

Sanjula dubey answered
To find the thickness of the metallic spherical shell, we need to use the concept of density and weight.

Given data:
- Weight of the metallic spherical shell = 11.176 kg
- Inner radius of the shell = 6 cm
- Density of the metal = 21 g/cm3

Let's solve the problem step by step:

1. Calculate the volume of the spherical shell:
The volume of a spherical shell can be calculated using the formula:
Volume = (4/3) * π * (R_outer^3 - R_inner^3)

Since the inner radius is given as 6 cm, we can assume the outer radius as R cm.

Volume = (4/3) * π * (R^3 - 6^3)

2. Calculate the weight of the metallic shell:
The weight of the metallic shell can be calculated using the formula:
Weight = Volume * Density

11.176 kg = Volume * 21 g/cm3

Now, let's convert the weight to grams:
11.176 kg = 11176 g

Therefore, Volume = 11176 g / 21 g/cm3

3. Substitute the value of Volume in the equation calculated in step 1 and solve for R:

11176 g / 21 g/cm3 = (4/3) * π * (R^3 - 6^3)

4. Simplify the equation:

(11176 g / 21 g/cm3) = (4/3) * π * (R^3 - 216)

5. Solve for R:

R^3 - 216 = (11176 g / 21 g/cm3) * (3/4π)

R^3 - 216 = 1596 g / 7 g/cm3

6. Simplify and solve for R:

R^3 = (1596 g / 7 g/cm3) + 216

R^3 = 228 g/cm3

Taking the cube root on both sides, we get:

R ≈ 6.2 cm

7. Calculate the thickness of the shell:

Thickness = R_outer - R_inner

Thickness = 6.2 cm - 6 cm

Thickness ≈ 0.2 cm

Therefore, the thickness of the metallic spherical shell is approximately 0.2 cm.

The height of a cone is 30 cm. A small cone is cut off at the top by a plane parallel to the base. If its volume be 1/27 of the volume of the given cone, at what height above the base is the section made?
  • a)
    20 cm
  • b)
    25 cm
  • c)
    10 cm
  • d)
    15 cm
Correct answer is option 'A'. Can you explain this answer?

Pragya joshi answered
Understanding the Problem
The problem involves a cone with a height of 30 cm, from which a smaller cone is cut off. The volume of this smaller cone is 1/27 of the volume of the original cone.
Volume of a Cone
The volume (V) of a cone is given by the formula:
- V = (1/3) * π * r² * h
where r is the radius and h is the height of the cone.
Volume Ratio of the Cones
Given that the volume of the smaller cone is 1/27 of the larger cone, we can express this mathematically:
- V_small = (1/27) * V_large
Relationship Between Heights and Volumes
Since the smaller cone is similar to the larger cone (as the cutting plane is parallel to the base), the ratio of their volumes relates to the ratio of their heights:
- V_small / V_large = (h_small / h_large)³
Let h_small be the height of the smaller cone, and h_large = 30 cm (the height of the larger cone).
Setting up the ratio:
- 1/27 = (h_small / 30)³
Solve for h_small
To find h_small, we take the cube root of both sides:
- h_small / 30 = (1/3)
Thus, h_small = 30 / 3 = 10 cm.
Height Above the Base
To find the height above the base where the section is made, we subtract the height of the smaller cone from the height of the larger cone:
- Height above base = h_large - h_small = 30 cm - 10 cm = 20 cm.
Conclusion
The section is made at a height of 20 cm above the base of the original cone. Thus, the correct answer is option 'A'.

A solid cylinder of diameter 12 cm and height 15 cm is melted and recast into 12 toys in the shape of a right circular cone mounted on a hemisphere. Find the radius of the hemisphere, if height of the cone is 3 times the radius.
  • a)
    3 cm
  • b)
    6 cm
  • c)
    5 cm
  • d)
    9 cm
Correct answer is option 'A'. Can you explain this answer?

Ritu Saxena answered
Radius of cylinder = 12/2 = 6 cm
height = 15 cm
Volume of cylinder = πr2h
= 22/7 x 6x 15
= 540π cm
Volume of 12 toys = 540π cm3
Volume of 1 toy = 540π/12 = 45π cm3
Let the radius of the hemisphere be r cm.
Height of the cone = 3r cm
Volume of one toy = Volume of hemisphere + volume of cone

Now

Five people will live in a tent. If each person requires 16 m2 of floor area and 100 m3 space for air then find the required height of the cone of the smallest size to accommodate those persons.
  • a)
    18.75 m
  • b)
    20 m
  • c)
    21.75 m
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Let the height of the required cone be h cm
∴ Required base area = (16) × 5
= 80 cm2 = πr2
Height = h  cm volume = 1/3 (πr2)h
According to given condition
Total volume required = 5 × 100 cm3 = 500 cm3

A cylindrical vessel of diameter 4 cm is partly filled with water. 300 lead balls are dropped in it. The rise in water level is 0.8 cm. The diameter of each ball is ____.
  • a)
    0.8 cm
  • b)
    0.4 cm
  • c)
    0.2 cm
  • d)
    0.5 cm
Correct answer is option 'B'. Can you explain this answer?

Ritu Saxena answered
Radius of vessel (R) = 2 cm 
Rise in water level = 0.8 cm
lume of water displaced by 300 lead balls
= πR2h = π x 4 x 0 .8 = 3.2m
∴ Volume displaced by one ball = 
Let radius of each ball be r cm .
∴ 
∴ Diameter = 2 x r= 0.4 cm

The ratio of the volumes of two spheres is 27 : 8. Find the ratio of their surface areas.
  • a)
    4 : 9
  • b)
    9 : 4
  • c)
    2 : 3
  • d)
    1 : 3
Correct answer is option 'B'. Can you explain this answer?

Ratio of volumes of spheres of radii r1 and r2 respectively

Similarly,
ratio of surface areas

According to condition

∴ Ratio of surface areas

The total surface area of a right cone is 1760 cm2 and the radius of its base is 14 cm. What is the lateral surface area of the cone?
  • a)
    1148 cm2
  • b)
    1144 cm2
  • c)
    1198 cm2
  • d)
    None of these
Correct answer is option 'D'. Can you explain this answer?

Swati verma answered
To find the lateral surface area of a cone, we need to know the slant height of the cone. However, the given information only includes the total surface area and the radius of the base.

Let's break down the formula for the total surface area of a cone:
Total Surface Area of Cone = Lateral Surface Area of Cone + Base Area of Cone

The base area of a cone is given by the formula:
Base Area of Cone = πr^2

Given that the radius of the base is 14 cm, we can calculate the base area:
Base Area of Cone = π(14 cm)^2 = 196π cm^2

Now, we can substitute the base area into the total surface area formula to find the lateral surface area:
1760 cm^2 = Lateral Surface Area of Cone + 196π cm^2

To find the lateral surface area, we need to isolate it on one side of the equation:
Lateral Surface Area of Cone = 1760 cm^2 - 196π cm^2

To calculate the value of the lateral surface area, we need to know the value of π (pi). However, the value of π is not given in the question. Therefore, we cannot determine the exact value of the lateral surface area.

Hence, the correct answer is option 'D' (None of these) since we do not have enough information to calculate the lateral surface area of the cone.

A cylinder, whose height is two-thirds of its diameter, has the same volume as a sphere of radius 4 cm. Calculate the radius of the base of the cylinder.
  • a)
    4 cm
  • b)
    5 cm
  • c)
    3 cm
  • d)
    6 cm
Correct answer is option 'A'. Can you explain this answer?

Given:
Height of the cylinder = 2/3 of its diameter

Volume of the cylinder = Volume of the sphere

To find: Radius of the base of the cylinder

Let's solve this step by step.

1) Formula for the volume of a cylinder is given by:
Volume = πr^2h, where r is the radius and h is the height.

2) Formula for the volume of a sphere is given by:
Volume = 4/3πr^3, where r is the radius of the sphere.

3) Since the volume of the cylinder is equal to the volume of the sphere, we can equate the two formulas:

πr^2h = 4/3πr^3

4) Canceling out π and dividing both sides by r^2, we get:

h = 4/3r

5) Given that the height of the cylinder is 2/3 of its diameter, which means h = 2/3d, where d is the diameter of the cylinder.

6) Substituting h = 2/3d in the equation from step 4, we get:

2/3d = 4/3r

7) Canceling out 2/3 on both sides and solving for r, we have:

d = 2r

r = d/2

8) Substituting r = d/2 in the equation from step 6, we get:

2/3d = 4/3(d/2)

9) Canceling out 2/3 on both sides and solving for d, we have:

1 = 4/3

This is not possible.

10) Therefore, the given information is inconsistent, and we cannot determine the radius of the base of the cylinder.

A hollow sphere of internal and external diameter 4 cm and 8 cm respectively is melted into a cone of base diameter 8 cm. Find the height of the cone.
  • a)
    12 cm
  • b)
    16 cm
  • c)
    14 cm
  • d)
    7 cm
Correct answer is option 'C'. Can you explain this answer?

Volume of the Hollow Sphere
To find the height of the cone formed by melting the hollow sphere, we first need to calculate the volume of the hollow sphere.
- External diameter: 8 cm
- Internal diameter: 4 cm
- External radius (R): 8 cm / 2 = 4 cm
- Internal radius (r): 4 cm / 2 = 2 cm
The volume of a hollow sphere is given by the formula:
Volume = (4/3)π(R³ - r³)
Calculating the volume:
- R³ = 4³ = 64
- r³ = 2³ = 8
- R³ - r³ = 64 - 8 = 56
Thus,
Volume of the hollow sphere = (4/3)π(56) = (224/3)π cm³
Volume of the Cone
Now, the volume of the cone formed from this hollow sphere is equal to the volume of the hollow sphere.
- Base diameter of the cone: 8 cm
- Radius of the cone (r_cone): 8 cm / 2 = 4 cm
Let the height of the cone be h. The volume of the cone is given by:
Volume = (1/3)πr_cone²h
Setting the volumes equal:
(224/3)π = (1/3)π(4²)h
Cancelling π and (1/3):
224 = 16h
Solving for h:
h = 224 / 16 = 14 cm
Conclusion
The height of the cone is 14 cm. Thus, the correct answer is option 'C'.

If the radius of a sphere is doubled then how many times will its surface area?
  • a)
    8
  • b)
    4
  • c)
    2
  • d)
    0.5
Correct answer is option 'B'. Can you explain this answer?

Surface area of sphere = 4πR2
If the radius of sphere is doubled, i.e., R becomes 2R, then
New surface area = 4π(2R)2 = 16πR2
= 4 (4πR2)
= 4 (surface area)
∴ Surface area will become 4 times.

Th e in terna l an d exte rn al dia mete rs of a hollow hemispherical vessel are 24 cm and 25 cm respectively. The cost to paint 1 cm2 of the surface is ₹ 0.05. Find the total cost to painting the vessel all over.
  • a)
    ₹ 108.32
  • b)
    ₹ 296.28 
  • c)
    ₹ 101.59
  • d)
    ₹ 96.28
Correct answer is option 'D'. Can you explain this answer?

Ritu Saxena answered
External radius of hemispherical vessel 
Internal radius of hemispherical vessel 
External curved surface area of hemispherical vessel = 2πr12
Internal curved surface area of hemispherical vessel = 2πr22
Area of top of the hemispherical vessel
Total surface area of the vessel
=
= 1925.78 cm2
Cost of painting the vessel at the rate of ₹ 0.05 per cm2 = 1925.78 » 0.05
= ₹ 96.28 

A cylindrical container is filled with icecream whose diameter is 12 cm and height 15 cm. The whole ice-cream cone?
  • a)
    6 cm
  • b)
    4 cm
  • c)
    8 cm
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Ritu Saxena answered
Let r be the radius of base of the conical part.
Height of the conical part = 4r
Volume of cone with hemispherical top = volume of cone + volume of hemispherical top

Volume of 10 such cones with hemispherical top
= 10 × 2πr3 = 20πr3 cm3
Volume of cylindrical container

20πr3 = 540π
r3 = 27 ⇒ r = 3 cm.
diameter = 3  × 2 = 6 cm

Find the maximum volume of a cone that can be carved out of a solid hemisphere of radius r.
  • a)
    4/3πr3
  • b)
    2πr3
  • c)
    1/3πr3
  • d)
    2/3πr3
Correct answer is option 'C'. Can you explain this answer?

To cut out maximum area, radius of the cone = radius of the hemisphere = r and height of the cone = radius of the hemisphere = r
∴ Volume of the cone = 1/3πr
2
h
= 1/3πr3

The number of solid spheres, each of diameter 6 cm that could be moulded to form a solid metal cylinder of height 45 cm and diameter 4 cm, is ____.
  • a)
    3
  • b)
    4
  • c)
    5
  • d)
    6
Correct answer is option 'C'. Can you explain this answer?

Vivek Bansal answered
Volume o f one solid sphere = 
Volume of cylinder = πr2h = π x 4 x 45
Now, Number of spheres x Volume of one sphere = Volume of cylinder
⇒ Number of spheres x 
⇒ Number of spheres = 45/9 = 5

A right cylinder, a right cone and a hemisphere have the same height and same base area. What is ratio of their volumes?
  • a)
    1 : 2: 3
  • b)
    3 : 1 : 2
  • c)
    2 : 3 : 1
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Ritu Saxena answered
Let the base areas and heights be A and h respectively.
For cylinder, volume = VC = πr2h = Ah
For cone, volume = VCO = 1/3 πr2h = 1/3 Ah
For hemisphere, volume = Vh = 2/3 πr3
∴ Ratio of their volumes = 2/3 (πr2)r
= 2/3 Ah [∵ h =r]

The surface area of the cylinder is 2992 cm2 and its height is 20 cm, what is the diameter of the cylinder?
  • a)
    14 cm
  • b)
    28 cm
  • c)
    7 cm
  • d)
    56 cm
Correct answer is option 'B'. Can you explain this answer?

Let r be the radius of the cylinder Total surface area = 2πr (h + r)

⇒ r2 + 20r - 476 = 0
⇒ r2 + 34r - 14r - 476 = 0
⇒ r(r + 34) - 14(r + 34) = 0
⇒ (r - 14) (r + 34) = 0
⇒ r = 14; r = -34 (Not possible)
diameter = 2 × 14 = 28 cm

To const ruct a wall 24 m long, 0. 4 m thick and 6 m high, bricks of diamensions 25 cm × 16 cm × 10 cm each are used. If the mortar occupies 1/10th of the volume of the wall, find the number of bricks used.
  • a)
    12960
  • b)
    14420
  • c)
    24566
  • d)
    14296
Correct answer is option 'A'. Can you explain this answer?

Ritu Saxena answered
Volume of the wall = 24 x 0.4 x 6 = 57.6m
Volume of mortar = 57.6/10 = 5.76 m3 
Volume of used bricks = (57.6 - 5.76) m= 51.84 m
Volume of each brick = (25 x 16 x 10) cm3 = 4000 cm3
∴ Number o f bricks used = 51.84 / 4/1000
= 12960

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