ML AGGARWAL CLASS 8 Chapter 18 Mensuration Exercise 18.3

  Exercise 18.3

Question 1

Sol :
Given volume of cube =343 cm3

Let 'S' be edge of cube 

Volume of cube = S3

s3=343S=3343S=7 cm.

ஃ Length of an edge of cube = 7cm


Question 2

Sol :

 (i) Volume of Cuboid    90 cm3    

Length 6cm   , Breadth  5cm  ,  Height  3cm


(ii) Volume of cuboid  840 cm3 

Length 15cm   , Breadth  15cm  ,  Height  7cm


(iii)  Volume of Cuboid   62.5 m3 

Length 10m   , Breadth  5m  ,  Height  1.25m


Question 3

Sol :

Given 

Volume of cuboid =312 cm3

Base Area=26 cm2

volume =312 cm

Area × height =312

26×h=312

h=31226

h = 12cm


Question 4

Sol :
Given 

Godown  dimension (1×b×h)= 55 m×45 m×30 m

Cuboidal box volume =1.25m3

 godown volume =l×b×h=55×45×30=74250 m3

No. of Cuboidal boxes =  godown Volume  box volune 

=742501.25

No. of cuboidal boxes =59400


Question 5

Sol :

Given Dimension of rectangular pit = 1.4 m×90 cm×70 cm

Volume of pit = l×b×h

=140×90×70 cm3

Volume of pit = 882000 cm3

Given 

Brick dimension (l × b) =2.1 cm×10.5 cm

Let 'h' height of brick 

1000× Brick volume = pit volume

1000×  21×10.5×h=882000

h=88200021×10.5×1000

h=4cm

Height of brick =4 cm


Question 6

Sol :
Let 'a' be edge of cube 

Volume of cube = a3

If each edge of cube is tripled = a1=3a

Volume of new Cube = a13

=(3a)3

=27a3

The Volume becomes 27 times the original Volume of Cube.

Question 7

Sol :
Given 

Milk tank is in the from of cylinder 

Diameter of tank = 1.4m × 2

Height of tank = 8m 

Volume of tank = πd2×h

π×(14)2×8

Volume of tank = 49 .260m3

∴ Volume of tank = 49.260 lit


Question 8

Sol :
Given 

Extended dimension of box = 84 cm×75 cm×64 cm

Thickness of box = 2 cm

∴ Internal Dimension of box = (542×2)cm , (75 - 2 × 2) cm ,(64- 2×2) cm

=80 cm×71 cm×60cm


Volume of wood = External Volume - Internal Volume 

= (84×75×64)(80×71×60)

403200340800

 Volume of wood =62400 cm3

Question 9

Sol :
Given 

Two Cylinder jar has same volume 

Let 

d1,d2 are diameter  jar

h1,h2 are heights of jar

Given 

d1:d23:4

Volume of cylinder equal

π4d21×h1=π4d22×h2

d21×h1=d22×h2

(d1d2)2=h2h1

(34)2=h2h1

h1h2=169

h1:h2=16:9

∴ Height of cylinders are in the ratio = 16: 9


Question 10

Sol :
Let   'r' be the ratio's of cylinder 

h be the height of cylinder 

Volume V = πr2×h

Now radius is  =R1=r2

Height is doubled = h1=2h

New Volume V1=πr21×h1

=π(r2)2×(2h)

=πr24×2h

v1=πr2×h2

v1=v2

ஃ New Volume is half of original Volume 


Question 11

Sol :

Dimensions of tin sheet =30 cm×18 cm

When rolled along its length (30cm)
-----------------------------------------------

2πr=30,h=18Cmr=302πr=4.77 cm

 Volume =πr2×h=π×4.772×18 Volume =1289.155 cm3


When rolled along breadth (18cm)
----------------------------------------------

2πr=18,h=30 lm

r=182π

r= 2.86 cm

 Volume =πr2×h=π×2.862×30=773.493 cm3

Question 12

Sol :
(i) Given dis of pipe = 7cm = 0.07m

Velocity = 5m\sec

Discharge = Area × Velocity 

=πd24×V

=π×(0.07)24×5

Discharge =0.0192 m3/sec

 Discharge =19.2 lits / see =19.2×60 lits /min

Discharge = 1154 .53 lits\min

Discharge 1155lit/min


(ii) Dimension of tank = 4m×3m×2.31m

Discharge =0.0192 m3/sec

1.154 m3/min

Time taken to fill the tank = Volume of tank  Discharge 

=4×3×2.311.154

Time taken to fill the tank = 24min

Question 13


Given 

Vessel 1 

radius 15cm 

Height 40cm 

Volume πxr2×h

π×(15)2+40

Volume 28274.33 cm3


Vessel 2

Radius  20cm

Height  40cm

Volume  πxr2×h 

π×(20)2+45

Volume  56548.667 cm3

Given 

Another vessel with capcity equal to sum of vessel 1 and vessel 2

Let radius of vessel's = R

Height of vessel = 30cm

(πR2)×30=28274.33+56548.667

30×(11R2)=84823R2=84823π×30

R2=900

R=900

R=30Cm

∴ Radius of vessel = 30cm

Question 14

Sol :
Given 

Pole height = 7m

Pole diameter = 20cm = 0.2m

Density = 225 kg/m3

Volume of wood = πd24×h

=π4(20)2104×7

Volume of wood =0.219 m3

Weight of wood = 49.48kg 

Question 15

Sol :








A cylinder with diameter of 14cm and height of 30cm is the maximum Volume 

That can be cut from given Cuboid 

Volume of cylinder = π4d2×h

=π4(14)2×30

Volume of cylinder = 4618.14 cm3

Volume of wood wasted = Volume of cuboid - Volume of cylinder 

14×14×30(4618.14)

Volume of Wood wasted = 1261.85 cm3

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