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 = a^{3}

If each edge of cube is tripled = a^{1}=3 a

Volume of new Cube = a^{1^{3}}

=(3 a)^{3}

=27 a^{3}

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 \times 2

Height of tank = 8m 

Volume of tank = \frac{\pi}{} d^{2} \times h

\frac{\pi}{} \times(1-4)^{2} \times 8

Volume of tank = 49 .260 m^{3}

∴ Volume of tank = 49.260 lit


Question 8

Sol :
Given 

Extended dimension of box = 84 \mathrm{~cm} \times 75 \mathrm{~cm} \times 64 \mathrm{~cm}

Thickness of box = 2 cm

∴ Internal Dimension of box = (54 -2\times 2)cm , (75 - 2 \times 2) cm ,(64- 2\times2) cm

=80 \mathrm{~cm} \times 71 \mathrm{~cm} \times 60 \mathrm{cm}


Volume of wood = External Volume - Internal Volume 

= (84 \times 75 \times 64)-(80 \times 71 \times 60)

403200-340800

 Volume of wood =62400 \mathrm{~cm}^{3}

Question 9

Sol :
Given 

Two Cylinder jar has same volume 

Let 

d_{1}, d_{2} are diameter  jar

h_{1,} h_{2} are heights of jar

Given 

d_{1}: d_{2} \cdot 3: 4

Volume of cylinder equal

\frac{\pi}{4} d_{1}^{2} \times h_{1}=\frac{\pi}{4} d_{2}^{2} \times h_{2}

d_{1}^{2} \times h_{1}=d_{2}^{2} \times h_{2}

\left(\frac{d_{1}}{d_{2}}\right)^{2}=\frac{h_{2}}{h_{1}}

\left(\frac{3}{4}\right)^{2}=\frac{h_{2}}{h_{1}}

\frac{h_{1}}{h_{2}}=\frac{16}{9}

h_{1}: h_{2}=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 = \pi r^{2} \times h

Now radius is  =R^{1}=\frac{r}{2}

Height is doubled = h^{1}=2 h

New Volume V^{1}=\pi r_{1}^{2} \times h^{1}

=\pi\left(\frac{r}{2}\right)^{2} \times(2 h)

=\frac{\pi r^{2}}{4} \times 2 h

v^{1}=\frac{\pi r^{2} \times h}{2}

v^{1}=\frac{v}{2}

ஃ New Volume is half of original Volume 


Question 11

Sol :

Dimensions of tin sheet =30 \mathrm{~cm} \times 18 \mathrm{~cm}

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

\begin{aligned} 2 \pi r &=30, \quad h=18 C m \\ r &=\frac{30}{2 \pi} \\ r &=4.77 \mathrm{~cm} \end{aligned}

\begin{aligned} \text { Volume } &=\pi r^{2} \times h \\ &=\pi \times 4.77^{2} \times 18 \\ \text { Volume } &=1289.155 \mathrm{~cm} 3 \end{aligned}


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

2 \pi r=18, \quad h=30 \mathrm{~lm}

r=\frac{18}{2 \pi}

r= 2.86 cm

\begin{aligned} \text { Volume } &=\pi r^{2} \times h \\ &=\pi \times 2.86^{2} \times 30 \\ &=773.493 \mathrm{~cm} 3 \end{aligned}

Question 12

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

Velocity = 5m\sec

Discharge = Area \times Velocity 

=\frac{\pi d^{2}}{4} \times V

=\frac{\pi \times(0.07)^{2}}{4} \times 5

Discharge =0.0192 \mathrm{~m}^{3} / \mathrm{sec}

\begin{aligned} \therefore \text { Discharge } &=19.2 \text { lits } / \text { see } \\ &=19.2 \times 60 \text { lits } / \mathrm{min} \end{aligned}

Discharge = 1154 .53 lits\min

Discharge \approx 1155 \operatorname{lit} / \min


(ii) Dimension of tank = 4 m \times 3 m \times 2.31 m

Discharge =0.0192 m^{3}/sec

1.154 \mathrm{~m}^{3} / \mathrm{min}

Time taken to fill the tank =\frac{\text { Volume of tank }}{\text { Discharge }}

=\frac{4 \times 3 \times 2.31}{1.154}

Time taken to fill the tank = 24min

Question 13


Given 

Vessel 1 

radius 15cm 

Height 40cm 

Volume \pi x r^{2} \times h

\pi \times(15)^{2}+40

Volume \quad 28274.33 \mathrm{~cm}^{3}


Vessel 2

Radius  20cm

Height  40cm

Volume  \pi x r^{2} \times h 

\pi \times(20)^{2}+45

Volume  56548.667 \mathrm{~cm}^{3}

Given 

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

Let radius of vessel's = R

Height of vessel = 30cm

\left(\pi R^{2}\right) \times 30=28274.33+56548.667

\begin{aligned} 30 \times\left(11 R^{2}\right) &=84823 \\ R^{2} &=\frac{84823}{\pi \times 30} \end{aligned}

R^{2}=900

R=\sqrt{900}

R=30 \mathrm{Cm}

∴ Radius of vessel = 30cm

Question 14

Sol :
Given 

Pole height = 7m

Pole diameter = 20cm = 0.2m

Density = 225 \mathrm{~kg} / \mathrm{m}^{3}

Volume of wood = \frac{\pi d^{2}}{4} \times h

=\frac{\pi}{4} \frac{(20)^{2}}{10^{4}} \times 7

Volume of wood =0.219 \mathrm{~m}^{3}

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 = \frac{\pi}{4} d^{2} \times h

=\frac{\pi}{4}(14)^{2} \times 30

Volume of cylinder = 4618.14 \mathrm{cm}^{3}

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

14 \times 14 \times 30-(4618.14)

Volume of Wood wasted = 1261.85 \mathrm{~cm}^{3}

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