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:

Consider the following statements:

1) The perimeter of a triangle is greater than the sum of its three medinas.

2) In any triangle ABC, if D is any point on BC, then AB + BC + CA > 2AD.

Which of the above statements is/are correct?

A) 1 only B) 2 only
C) Both 1 and 2 D) Neither 1 nor 2
 
Answer & Explanation Answer: C) Both 1 and 2

Explanation:
Let ABC be the triangle and D. E and F are midpoints of BC, CA and AB respectively.
Recall that the sum of two sides of a triangle is greater than twice the median bisecting the third side,(Theorem to be remembered)
Hence in ΔABD, AD is a median
AB + AC > 2(AD)
Similarly, we get
BC + AC > 2CF
BC + AB > 2BE
On adding the above inequations, we get
(AB + AC) + (BC + AC) + (BC + AB )> 2AD + 2CD + 2BE
2(AB + BC + AC) > 2(AD + BE + CF)
AB + BC + AC > AD + BE +CF
 
2.
To prove: AB + BC + CA > 2AD
Construction: AD is joined
Proof: In triangle ABD,
AB + BD > AD [because, the sum of any two sides of a triangle is always greater than the
third side]
----
1
In triangle ADC,
AC + DC > AD [because, the sum of any two
sides of a tri
angle is always greater than the
third side]
----
2
Adding 1 and 2 we get,
AB + BD + AC + DC > AD + AD
=> AB + (BD + DC) + AC > 2AD
=> AB + BC + AC > 2AD
Hence proved
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1 19401
Q:

The size of the wooden block is 5 x 10 x 20 cm .How many such blocks will be required to construct a solid wooden cube of minimum size? 

A) 6 B) 8
C) 12 D) 16
 
Answer & Explanation Answer: B) 8

Explanation:

Side of smallest cube = L.C.M of 5, 10, 20 = 20cm  

Volume of the cube = (20 x 20 x 20)cu.cm = 8000 cu.cm  

Volume of the block= (5 x 10 x 20)cu.cm = 1000 cu.cm  

Number of blocks = (8000/1000) = 8

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35 19104
Q:

In the figure AMB = 130°, then what is the value (in deg) of ABQ?

 

A) 40 B) 50
C) 60 D) 90
 
Answer & Explanation Answer: B) 50

Explanation:
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3 18790
Q:

Find the volume (in cm3) of a right circular cone of diameter 7 cm and height 7 cm.

 

A) 69.06   B) 16.43  
C) 11.15   D) 89.83
 
Answer & Explanation Answer: D) 89.83

Explanation:
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0 17968
Q:

A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8g/cu.cm, then the weight of the pipe is

A) 3.6 kg B) 3.696 kg
C) 36 kg D) 36.9 kg
 
Answer & Explanation Answer: B) 3.696 kg

Explanation:

External radius = 4 cm 

Internal radius = 3 cm 

Volume of iron = 227×42-32×21cm3462cm3   

Weight of iron = (462 x 8)gm = 3696 gm = 3.696 kg

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28 17416
Q:

Find the volume (in cub.cm) of a hemisphere of diameter 28 cm.

 

A) 4789.67   B) 3675  
C) 2732 D) 5749.33
 
Answer & Explanation Answer: D) 5749.33

Explanation:
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1 17160
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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1 17112
Q:

∆DEF is right angled at E. If m∠F = 45°, then find the value of (tanD - √3/2).

 

A) -√3/2 B) -1/2√3
C) (2-√3)/2 D) (3√3-1)/3
 
Answer & Explanation Answer: C) (2-√3)/2

Explanation:
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0 17074