Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

Mathematics (Maths) Class 9

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Class 9 : Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

The document Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev is a part of the Class 9 Course Mathematics (Maths) Class 9.
All you need of Class 9 at this link: Class 9

Question 1. What is the longest pole that can be put in a room of dimensions l = 10 cm, b = 10 cm and h = 5 cm?
 Solution: 
The longest diagonal of a cuboid =Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

∴ The length  of the required pole (diagonal) = Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

 

Question 2. Total surface area of a cube is 96 cm2. What is its volume?
 Solution:
Total surface area of the cube = 6l2

∴   Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

Thus, the volume of the cube = l3 = 43 = 64 cm


Question 3. The radius of a sphere doubled. What per cent of its volume is increased?
 Solution:
Original volume = (4/3)πr3

Increased volume = (4/3)π(2r)3 = 32/3πr3

Increase in volume =  32/3πr3 -  4/3πr3 = 28/3πr3

∴ Per cent increase in volume = Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

 

Question 4. Write ‘True or False’ for the following statements: (i) A right circular cylinder just encloses a sphere of radius r as shown in the figure. The area of the sphere is equal to the curved surface area of the cylinder.
 Solution:
True.

∵ [Radius of the sphere] = [Radius of the cylinder] = r

Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

∴ Diameter of the sphere = 2r
⇒ Height of the cylinder (h) = 2r
Now, surface area of the sphere = 4πr
And curved surface area of the cylinder = 2πrh = 2πr (2r) = 4πr2

(ii) An edge of a cube measures ‘r’ cm. If the largest possible right circular cone is cut out of this cube, then the volume of the cone (in cm3) is 1/6πr3
Solution: False.
∵ Height of the cone = r cm
∴ Diameter of the base of the cone = r cm

⇒ Radius of the base of the cone = (r/2) cm

Now volume of the cone Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

 

Question 5. If the total surface area of a sphere is 154 cm2. Find its total volume.
 Solution:
Let ‘r’ be radius of the sphere
∴ Total S.A. = 4 π r2 = 154 cm2

Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

or        Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

Now,                 Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

 

Question 6. If the radius of a sphere is 3r then what is its volume?
 Solution:

Very Short Answers Type Questions- Surface Areas and Volumes Class 9 Notes | EduRev

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