Volume and Surface Area Questions

FACTS  AND  FORMULAE  FOR  VOLUME  AND  SURFACE  AREA  QUESTIONS

 

 

I. CUBOID

   Let length=l, breadth =b and height =h units. Then,

1. Volume = (l x b x h)

2. Surface area = 2(lb +bh + lh) sq.units

3. Diagonal =l2+b2+h2 units

 

 

II. CUBE 

Let each edge of a cube be of length a. Then,

1. Volume = a3 cubic units.

2. Surface area = 6a2 sq.units

3. Diagonal = 3a units

 

 

III. CYLINDER 

Let radius of base = r and Height (or Length) = h. Then, 

1.Volume = πr2h cubic units 

2. Curved surface area = 2πrh sq.units

3. Total surface area = 2πrh+2πr2 sq.units

 

 

IV. CONE 

Let radius of base =r and Height = h. Then, 

1. Slant height, l=h2+r2 units

 

2. Volume = 13πr2h cubic units.

 

3. Curved surface area = πrlsq.units 

 

4. Total surface area = πrl+πr2sq.units

 

 

V. SPHERE 

Let the radius of the sphere be r. Then, 

1. Volume =43πr3 cubic units

2. Surface area = 4πr2 sq.units

 

 

VI. HEMISPHERE 

Let the radius of a hemisphere be r. Then, 

1. Volume = 23πr3 cubic units.

2. Curved surface area = 2πr2 sq.units

3. Total surface area = 3πr2 sq.units

 

Q:

Which of the following statement is CORRECT about the tangents?

 

A) The tangents drawn at the end of diameter of a circle are parallel to each other.   B) The line segment which joins the point of contact of two parallel tangents to the circle is the diameter of the circle.  
C) Tangents drawn from the external points subtends equal angle at the center.   D) All option are correct.  
 
Answer & Explanation Answer: D) All option are correct.  

Explanation:
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Q:

A cube is inscribed in a sphere. A right circular cylinder is within the cube touching all the vertical faces. A right circular once is inside the cylinder. Their heights are same and the diameter of the cone is equal to that of the cylinder.

What is the ratio of the volume of the sphere to that of cone?

A) 6√3:1 B) 7 : 2
C) 3√3:1   D) 5√3:1
 
Answer & Explanation Answer: A) 6√3:1

Explanation:
The top view of the given assembly will look like the figure above
Outermost is the sphere. Inside that there is a cube and within that there is a cone and cylinder with same radius.
Here side of cube = a
Diameter of Sphere = body diagnol = √3 a
Radius of sphere = √3 a/2 =r1
Height of Cylinder = Height of cone = side of cube = a =h
Radius of cylinder = Radius of cone = side of cube/2 = a/2 =r2(as shown in the figure)
Volume of sphere/volume of cone = 43πr1313πr22h = 6√3:1
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1 2386
Q:

Solve the triangle b=36 a=38 c=18 for perimeter of the triangle?

A) 74 units B) 92 units
C) 56 units D) 54 units
 
Answer & Explanation Answer: B) 92 units

Explanation:

We know, the perimeter of a triangle = sum of all the sides of a triangle = a + b + c

 

Here given that sides a = 38, b= 36 and c = 18

solve_the_triangle_b36_a38_c181537423406.jpg image

 

Now, perimeter of the triangle = a + b + c = 38 + 36 + 18 = 92 units.

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5 2208
Q:

What is the percentage decrease in the area of a triangle if its each side is halved?

A) 75% B) 50%
C) 25% D) No change
 
Answer & Explanation Answer: A) 75%

Explanation:
Area of triangle of = ½*a*b* sinθ = A
Where a and b are sides of the triangle and θ be the angle between them
After decreasing each side
New area = ½*(a/2)*(b/2)*sinθ = ¼ A
%decrease = [(A–¼ A)/A ]*100 = 75%
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1 2135
Q:

The areas of three consecutive faces of a cuboid are 12 cm², 20cm² and 15 cm², then the volume (in cm³) of the cuboid is

A) 60 B) 55
C) 45 D) 40
 
Answer & Explanation Answer: A) 60

Explanation:

From the given data,

let the length, breadth and height of the cuboid are m, n, r

m x n = 12

n x r = 20

r x m = 15

 

Hence, m x n x n x r x r x m = 12 x 20 x 15

mnr = sqrt of (12x20x15) = 60 cub.cm.

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11 2133
Q:

A right triangular prism has equilateral triangle as its base. Side of the triangle is 15 cm. Height of the prism is 20√3 cm. What is the volume (in cm3) of the prism?

A) 1125 B) 6750
C) 4500 D) 3375
 
Answer & Explanation Answer: D) 3375

Explanation:
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Q:

If the radius of the cylinder is increased by 25%, then by how much percent the height must be reduced, so that the volume of the cylinder remains same?

A) 36 B) 56
C) 64 D) 46
 
Answer & Explanation Answer: A) 36

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Q:

Three circle C1, C2 and C3 with radii r1, r2 and r3 (where r1<r2<r3) are placed as shown in the given figure. What is the value of r2?

A) √( r1r3) B) ( r1 + r3)/2
C) (2 r1r2)/( r1 + r2) D) √( r1 + r3)
 
Answer & Explanation Answer: A) √( r1r3)

Explanation:
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